Pair Handel System And Metoden

Hemligheten att hitta vinst i parhandel. Quants är Wall Streets namn för marknadsforskare som använder kvantitativ analys för att utveckla lönsamma handelsstrategier. Kort sagt, en kvantkammar genom prisförhållanden och matematiska relationer mellan företag eller handelsfordon för att gudomliga lönsamma handelsmöjligheter. Under 1980-talet var en grupp quants Arbeta för Morgan Stanley slog guld med en strategi som kallas parhandel Institutionella investerare och proprietära handelsdiskar hos stora investeringsbanker har använt tekniken ända sedan och många har gjort en snygg vinst med strategin. Det är sällan i bästa intresse av investeringsbanker och fondförvaltare att dela med sig av lönsamma handelsstrategier med allmänheten, så parhandeln var en hemlighet för proffsen och några fåtaliga individer fram till internetens tillkomst. Onlinehandel öppnade locket på realtidsinformation och gav nybörjare tillgång till alla typer av investeringsstrategier Det tog inte lång tid för parhandeln att attrahera ct enskilda investerare och småföretagare som försöker säkra deras riskexponering mot rörelserna på den bredare marknaden. Vad är Par Trading. Pairs trading har potential att uppnå vinst genom enkla och relativt låga riskpositioner Parhandeln är marknadsneutral vilket betyder att den globala marknadens riktning inte påverkar sin vinst eller förlust. Målet är att matcha två handelsfordon som är starkt korrelerade, handla en lång och den andra kort när parets prisförhållande avviker x antal standardavvikelser - x är optimerad med historiska data Om paret återgår till sin genomsnittliga trend görs en vinst på en eller båda positionerna. Ett exempel med Stocks. Traders kan använda antingen grundläggande eller tekniska data för att konstruera en parhandelstyp. Vårt exempel här är tekniskt in Natur men vissa handlare använder ett PE-förhållande eller andra grundläggande faktorer för att mäta korrelation och divergens. Det första steget i att utforma en parhandel är att hitta två bestånd som är starkt korrelerade d Vanligtvis betyder det att företagen är i samma bransch eller delsektor, men inte alltid. Exempelvis kan indexspårningslager som QQQQ Nasdaq 100 eller SPY SP 500 erbjuda bra parhandelsmöjligheter. Två index som i allmänhet handlar ihop är de SP 500 och Dow Jones Utilities Average Denna enkla prissituation för de två indexen visar deras korrelation. För vårt exempel kommer vi att titta på två företag som är mycket korrelerade GM och Ford Eftersom båda är amerikanska bilprodusenter tenderar deras lager att röra sig tillsammans. Below är ett veckovis diagram över prisförhållandet mellan Ford och GM beräknat genom att dividera Ford s aktiekurs genom GM s aktiekurs. Detta prisförhållande kallas ibland relativ prestanda, inte förväxlas med det relativa styrka indexet något helt annat. Den centrala vita linjen Representerar det genomsnittliga prisförhållandet de senaste två åren De gula och röda linjerna representerar en och två standardavvikelser från medelvärdet, respekterar Y. I diagrammet nedan kan potentialen för vinst identifieras när prissättningsgraden träffar sin första eller andra avvikelse. När dessa lönsamma skillnader uppträder är det dags att ta en lång position i underpresteraren och en kort position i överköpet. Intäkterna från Den korta försäljningen kan hjälpa till att täcka kostnaden för den långa positionen, vilket gör paren handel billigt att sätta på. Ställningsstorlek för paret bör matchas med dollarvärde i stället för antal aktier så är en 5-steg i en lika med en 5-steg i Andra Som med alla investeringar finns det risk för att affärerna kan röra sig in i rött, så det är viktigt att bestämma optimerade stopp-poäng innan man genomför parhandel. Ett exempel med framtida kontrakt. Parhandelsstrategin fungerar inte bara med Lager, men även med valutor, råvaror och till och med alternativ På terminsmarknaden är mini-kontrakt - mindre kontrakter som utgör en bråkdel av värdet av fullstorlek - möjliggör mindre investerare att handla i terminer. En parhandel på terminsmarknaden kan innebära en arbitrage mellan terminsavtalet och kontantpositionen för ett visst index. När terminsavtalet går före kontantpositionen kan en näringsidkare försöka dra nytta av att korta framtiden och Det går ofta länge i indexspårningsstocken och förväntar sig att de kommer samman vid en viss tid. Vanligtvis är rörelserna mellan ett index eller en vara och dess terminsavtal så täta att vinsterna bara lämnas för de snabbaste av handlare - ofta använder datorer för att automatiskt utföra enorma positioner Vid ett ögonblick. Ett exempel använder Options. Option handlare använder samtal och sätter för att säkra risker och utnyttja volatilitet eller bristen på det. Ett samtal är ett åtagande från författaren att sälja aktier i ett lager till ett visst pris någon gång i framtiden En uppsättning är ett åtagande av författaren att köpa aktier till ett visst pris någon gång i framtiden. En parhandel på optionsmarknaden kan innebära att man gör ett samtal för en säkerhet som överträffar sin pappa Ir en annan högt korrelerad säkerhet och matchar positionen genom att skriva en uppsättning för paret den underpresterande säkerheten Eftersom de två underliggande positionerna återgår till deras medelvärde igen blir alternativen värdelösa så att näringsidkaren kan fälla upp vinsten från en eller båda positionerna. Bevis på lönsamhet. I juni 1998 släppte Yale School of Management ett dokument som skrevs av Even G Gatev, William Goetzmann och K Geert Rouwenhorst som försökte bevisa att parhandeln är lönsam. Med hjälp av data från 1967 till 1997 fann trioen att över en sexmånaders handelsperiod, varpar paren i genomsnitt en tolv avkastning. För att skilja lönsamma resultat från slumpen, inkluderade deras test konservativa uppskattningar av transaktionskostnader och slumpmässigt utvalda par. Du kan hitta hela 34-sidiga dokumentet här. De är intresserade av paren Trading teknik kan hitta mer information och instruktion i Ganapathy Vidyamurthy s bok Pairs Trading Kvantitativa metoder och analys som du kan hitta henne E. Den breda marknaden är full av ups och downs som tvingar ut svaga spelare och konfronterar även de smartaste prognosticatorerna. Lyckligtvis använder man marknadsneutrala strategier som parhandeln, investerare och handlare kan hitta vinster under alla marknadsförhållanden Parternas skönhet handlar Är dess enkelhet Den långa korta förhållandet mellan två korrelerade värdepapper verkar som en ballast för en portfölj som fångas i den häftiga vattnet i den övergripande marknaden Lycka till med din jakten på vinst i parhandel och här är din framgång på marknaderna. mängden pengar som Förenta staterna kan låna Skuldtaket skapades enligt Second Liberty Bond Act. Räntesatsen vid vilken ett förvaringsinstitut lånar medel som förvaras i Federal Reserve till ett annat förvaringsinstitut.1 En statistisk åtgärd av spridning av avkastning för ett givet säkerhets - eller marknadsindex Volatilitet kan antingen mätas. En akt som den amerikanska kongressen antog 1933 som banklagen, som förbjöd kommersiell b Ankar från att delta i investeringen. Nonfarm lön hänvisar till något jobb utanför gårdar, privata hushåll och nonprofit sektorn Den amerikanska presidiet för arbete. Valutakortet eller valutasymbolen för den indiska rupien INR, indiens valuta Rupén består av av 1.A metod tillhandahålls för att uppfylla en parhandelförfrågan och innefattar stegen att mottaga ett flertal parhandelstillägg, som utför en transaktion för en första del av ett av flera parhandelstillägg och matchar en andra del av den ena av Flertalet parhandel begär mot en annan av de flesta parhandelstillägg. 46.1 En datorimplementerad metod för att uppfylla ett parhandelskrav, innefattande stegen att: ta emot ett flertal parhandelskrävningar, innefattande ett parhandelsförfrågan och ett annat parhandelskrav, varvid varje parhandelstillägg innefattar en begäran att handla en första säkerhet, En begäran om handel med en andra säkerhet och en begäran om handel med nämnda första säkerhet och nämnda andra säkerhet med en minsta spridningsgräns och varvid den första säkerheten och den andra säkerheten vardera har ett budpris och ett askpris. på marknaden för den första säkerheten och den andra säkerhetsbestämningen frågar frågan spridningen på marknaden för den första säkerheten och den andra säkerheten. bestämmer att minsta spridningsgränsen för varje parhandelsförfrågan är uppfylld av ett antal budbudsfördelningar Och sagda fråga fråga spridning exekvering av en transaktion mellan en första del av handeln med nämnda första säkerhet i nämnda begäran om ett parhandel och åtminstone en begäran om icke-parhandel, försörjning ed att den minsta spridningsgränsen för nämnda begäran om ett parhandel är uppfylld av nämnda intervall av budbudsfördelningen och nämnda fråga frågar spridning och sammankoppling, med användning av en dator, en andra del av handeln hos nämnda första säkerhet i nämnda ett parhandel begära och åtminstone en första del av handeln med den andra säkerheten i nämnda enkla handelsförfrågan mot nämnda andra handelsförfrågan, förutsatt att ett intervall av minsta spridningsgränsen för nämnda begäran om ett parhandel och nämnda andra handelsförfrågan överlappar varandra med nämnda intervall av budgivningsfördelningen och nämnda frågfråga spridning. 2. Förfarande enligt patentkrav 1, varvid steget att exekvera en transaktion för den första delen av handeln med den första säkerheten i nämnda enkla handelsförfrågan innefattar steget att exekvera en Transaktion för nämnda första del av handeln med den första säkerheten i nämnda begäran om ett parhandel på en extern marknad. 3. Sättet enligt krav 1, varvid steget att exekvera en transaktion utförs av en finansiell institution h Avgivning av en orderinventering och steget att utföra en transaktion innefattar steget att exekvera en transaktion för nämnda första del av handeln med den första säkerheten i nämnda ettparhandelskrav mot nämnda orderinventering.4. Sättet enligt patentkrav 1 innefattar vidare. utförande av en transaktion mellan en andra del av handeln med den andra säkerheten i nämnda begäran om ett parhandel och åtminstone en annan begäran om icke-parhandel, under förutsättning att minsta spridningsgränsen för nämnda begäran om ett parhandel är uppfylld av nämnda utbud av budet Budspridning och nämnda fråga frågar spridning och varvid steget att exekvera nämnda första del av nämnda 1-par-handelsförfrågan och exekvera nämnda andra del av nämnda begäran om ett parhandel innefattar stegen att bestämma huruvida budpriset för den första säkerheten och Budpriset för den andra säkerheten uppfyller en spridningsgräns. Bestämmer ett belopp för den andra säkerheten som kan säljas baserat på en budstorlek som är associerad med den andra säkerheten. beräkning av ett ekvivalent utlåning av den första säkerhet som kan köpas baserat på mängden av nämnda andra säkerhet som kan säljas. justering av motsvarande ekvivalent mängd av nämnda första säkerhet baserad på justeringskriterier. beräkning av ett inköpspris för nämnda justerade ekvivalenta mängd av nämnda första säkerhetsbaserade på spridningsgränsen. exekvering av en initierande ordning för att köpa nämnda justerade ekvivalenta mängd av nämnda första säkerhet vid nämnda inköpspris och exekvera en täckningsorder för att sälja nämnda mängd av den andra säkerheten. 5. Förfarande enligt krav 4, varvid steget att exekvera en täckande order att sälja innefattar steget att exekvera en täckningsorder för att sälja nämnda mängd av den andra säkerheten till anbudspriset för den andra säkerheten.6. Sättet enligt patentkrav 4, vidare innefattande stegen att bestämma huruvida frågans pris på den första Säkerhet och frågepriset för den andra säkerheten uppfyller en spridningsgräns. Bestämmer ett belopp för den första säkerheten som kan köpas baserat på en erbjudandestorlek som är associerad med den första satsen Curity. calculating en motsvarande mängd av den andra säkerheten som kan säljas baserat på mängden av den andra säkerheten som kan köpas. Justering av motsvarande mängd av den andra säkerheten baserad på justeringskriterier. Beräkning av ett försäljningspris för den justerade ekvivalenta mängden nämnda andra säkerhet baserad på spridningsgränsen exekvering av en initierande ordning för att sälja den justerade ekvivalenta mängden av nämnda andra säkerhet till nämnda försäljningspris och exekvera en täckningsorder för att köpa nämnda mängd av den första säkerheten. 7. Sätt enligt krav 6, varvid steg för att genomföra en täckningsorder för inköp innefattar steget att exekvera en täckningsorder för att köpa nämnda mängd av den första säkerheten vid askpriset för den första säkerheten.8. Sätt enligt krav 6, varvid justeringskriterierna innefattar en minsta mängd och en maximalt belopp. 9. Förfarande enligt krav 8, varvid steget att exekvera en initierande ordning innefattar steget att kringgå nämnda initierande ordning till en rund lotstorlek . 10. Förfarande enligt krav 1, varvid steget att exekvera en första del av handeln med den första säkerheten i nämnda begäran om ett parhandel innefattar steget att exekvera en första del av handeln med den första säkerheten i nämnda begäran om ett parhandel i ett flertal trancher. 11. Förfarande enligt patentkrav 1, varvid nämnda 1-par-handelsförfrågan har en första spridningsgräns och nämnda andra parhandelstillägg har en andra spridningsgräns och varvid steget att matcha nämnda andra del av nämnda handel med nämnda första säkerhet i nämnda ett-par-handelsförfrågan och åtminstone en första del av handeln med den andra säkerheten i nämnda handelsförfrågan mot nämnda andra par, innefattar vidare stegen att bestämma att ett intervall av nämnda första spridningsgräns och den andra spridningen Begränsa överlappningar med en marknadsspridning. Sätta en spridningsnivå. Beräkna priser för den första säkerheten och den andra säkerheten som ligger inom marknaden spridas och baseras på nämnda spridningsnivå och Den andra delen av handeln med den första säkerheten i nämnda begäran om ett parhandel och åtminstone en första del av handeln med den andra säkerheten i begäran om ett parhandel mot nämnda andra parhandelstillägg baserat på de beräknade priserna. Patentkrav 11, varvid steget att ställa in en spridningsnivå innefattar stegen att beräkna ett medelvärde mellan nämnda första spridningsgräns och nämnda andra spridningsgräns och att sätta nämnda spridningsnivå som nämnda, om nämnda medelvärde ligger inom nämnda marknadsspridning. krav 12 vidare innefattande steget att identifiera ett spridningsbelopp som är närmast nämnda medelvärde och inom nämnda marknadsspridning och att sätta nämnda spridningsnivå som nämnda spridningsbelopp om nämnda medel inte ligger inom nämnda marknadsspridning. 14. Sätt enligt krav 1, varvid Nämnda ett-par-handelsförfrågan har en första spridningsgräns, ett inköpsförhållande och ett försäljningsförhållande, nämnda andra handelsförfrågan har en andra spridningsgräns, ett köpförhållande och ett försäljningsförhållande och varvid steget att matcha en andra port Jon av nämnda handel med nämnda första säkerhet i nämnda begäran om ett parhandel och åtminstone nämnda första del av handeln med nämnda andra säkerhet i nämnda ettparhandelskrav mot nämnda andra handelsförfrågan inkluderar vidare stegen att bestämma att nämnda köpförhållande Och nämnda försäljningsförhållande som är associerat med nämnda en handelsförfrågan är inte lika med nämnda köpförhållande och nämnda försäljningsförhållande för nämnda andra parhandelstillägg och att en överlappning existerar mellan intervallet av nämnda första spridningsgräns och den andra spridningsgränsen och en marknadsspridning. att marknadspriserna existerar inom överlappningen. bestämmer ett felmatchningsbelopp i den andra säkerheten baserat på en skillnad mellan nämnda köpförhållande och nämnda försäljningsförhållande som är associerat med nämnda ett parhandelsförfrågan och nämnda köpförhållande och nämnda försäljningsförhållande för nämnda andra parhandel request. calculating ett korsbelopp för nämnda första säkerhet och nämnda andra säkerhet. selekterande ett korsningspris för nämnda första säkerhet och nämnda andra säkerhet som är inom nämnda överlappning. detektering av att nämnda felaktiga mängd är tillgänglig vid nämnda övergångspris för nämnda andra säkerhetsmatchning nämnda andra del av handeln hos den första säkerheten i nämnda ettparhandelstillägg och åtminstone nämnda första del av handeln med nämnda andra säkerhet I nämnda ett par-handelsförfrågan mot nämnda andra par-handelsförfrågan baserad på nämnda valda priser och exekvering av en transaktion för nämnda felaktiga mängd av nämnda andra säkerhet vid nämnda övergångspris för nämnda andra säkerhet. 15. Förfarande enligt krav 14, varvid steget att bestämma att nämnda otillbörliga matchningsbelopp är tillgängligt vid nämnda övergångspris för nämnda andra säkerhet innefattar steget att bestämma att nämnda otillbörliga matchningsbelopp är tillgängligt på en extern marknad vid nämnda övergångspris för nämnda andra säkerhet. 16. Förfarande enligt krav 14, varvid steget att bestämma att nämnda felaktiga mängd är tillgängligt utförs av en finansiell institution som har en orderinventering och steget att bestämma det nämnda Mismatch-beloppet är tillgängligt vid nämnda övergångspris för nämnda andra säkerhet innefattar steget att bestämma att nämnda otillbörliga matchningsbelopp är tillgängligt i nämnda orderinventering vid nämnda övergångspris för nämnda andra säkerhet. 17. Förfarande enligt patentkrav 1, varvid nämnda ettparhandelstillägg och nämnda andra handelsförfrågan anger ett antal spridningar och varvid steget att matcha en andra del av handeln med den första säkerheten i nämnda begäran om ett parhandel och åtminstone den första delen av handeln med den andra säkerheten i nämnda ett parhandel förfrågan mot nämnda andra par-handelsförfrågan inkluderar steget att matcha en andra del av handeln med den första säkerheten i nämnda begäran om ett parhandel och åtminstone nämnda första del av handeln med den andra säkerheten i nämnda enkla handelsförfrågan mot Sade ett annat par-handelsförfrågan om nämnda antal spridningar är större än ett minimalt antal spreads.18. Förfarande enligt krav 1 innefattande steget att mottaga en preferens För att fylla åtminstone en del av nämnda flertal handelsförfrågningar via exekveringssteget. 19. Sätt enligt krav 1 innefattande steget att mottaga en preferens för att fylla åtminstone en del av nämnda flertal handelsförfrågningar via matchningssteget. 20 Metoden för krav 1, varvid en klient skickar en fråga angående en status för nämnda parhandelstillägg och statusen för nämnda parhandelskrav uppdateras kontinuerligt i realtid.21. Förfarande enligt patentkrav 19, varvid preferensen är inlämnad av en klient elektroniskt.22 Metoden Enligt krav 1, varvid en klient mottar en simultan rapport när nämnda parhandelstillägg fylls och klienten bekräftar nämnda parhandel elektroniskt.23. Förfarande enligt patentkrav 1, vidare innefattande exekvering av en transaktion mellan en andra del av handeln hos den andra säkerheten i Nämnda ett-par-handelsförfrågan och åtminstone en annan begäran om icke-parhandel, under förutsättning att den minsta spridningsgränsen för nämnda begäran om ett parhandel är uppfylld av nämnda intervall av budgivningsbudet D och nämnda fråga frågar spridning och varvid steget att exekvera nämnda första del av nämnda 1-par-handelsförfrågan och exekvering av nämnda andra del av nämnda 1-par-handelsförfrågan inkluderar steget att bestämma huruvida frågpriset för den första säkerheten och frågan Priset för den andra säkerheten uppfyller en spridningsgräns. Bestämmer ett belopp för den andra säkerheten som kan köpas baserat på en frågestorlek som är associerad med den andra säkerheten. Beräknar en motsvarande mängd av nämnda första säkerhet som kan säljas baserat på mängden av sekundär säkerhet som kan köpas. justera nämnda ekvivalenta mängd av nämnda första säkerhet baserad på justeringskriterier. beräkning av ett försäljningspris för nämnda justerade ekvivalenta mängd av nämnda första säkerhet baserat på spridningsgränsen. exekvering av en initierande order för att sälja den justerade ekvivalenta mängden sa första säkerhet till sagda försäljningspris och exekvera en täckningsorder för att köpa nämnda mängd av nämnda andra säkerhet.24 Ett system för att uppfylla ett par trad E-begäran, varvid systemet mottar ett flertal parhandelstillägg, innefattande ett parhandelsförfrågan och ett annat parhandelskrav, varvid varje parhandelstillägg innefattar en begäran att handla en första säkerhet, en begäran att handla en andra säkerhet och en begäran att handla den första säkerheten och den andra säkerheten med en minsta spridningsgräns, och där den första säkerheten och den andra säkerheten vardera har ett budpris och ett askpris, innefattande ett parhandelsmotor för att bestämma budspridningen på marknaden för Sade den första säkerheten och den andra säkerheten. Bestämmer frågan fråga spridning på marknaden av den första säkerheten och den andra säkerheten. Bestämmer att minsta spridningsgränsen för varje parhandelskrav begärs uppfylls av ett antal nämnda budbudspridning och nämnda fråga fråga Spridas för varje säkerhet som exekverar en transaktion mellan en första del av handeln med nämnda första säkerhet i nämnda begäran om ett parhandel och åtminstone en begäran om icke-parhandel, under förutsättning att mini mumspridningsgränsen för nämnda 1-par-handelsförfrågan uppfylls av nämnda intervall av budspridningsspridningen och nämnda frågespridnings-spridning och ett parövergångsnät för att matcha en andra del av nämnda handel med nämnda första säkerhet i nämnda begäran om ett parhandel och vid Åtminstone en första del av handeln med nämnda andra säkerhet i nämnda enkla handelsförfrågan mot nämnda andra parhandelstillägg, förutsatt att ett intervall av minsta spridningsgränsen för nämnda begäran om ett parhandel och nämnda andra parhandelstillägg överlappar varandra med nämnda intervall av Nämnda bud bud spridas och sagda fråga fråga spridning.25 Systemet enligt patentkrav 24 vidare innefattande en länk till en extern marknad där nämnda parhandelsmotor vidarebefordrar transaktionen för den första delen av handeln med den första säkerheten i nämnda begäran om ett parhandel för Utförande på den externa marknaden via nämnda länk.26 Systemet enligt patentkrav 24, vidare innefattande en finansiell institution som har en orderinventering och varvid nämnda parhandelsmotor utför nämnda transaktion n för nämnda första del av handeln med den första säkerheten i nämnda enkla handelsförfrågan mot nämnda orderinventering.27 Systemet enligt patentkrav 24, varvid nämnda parhandelsmotor bestämmer huruvida budpriset för den första säkerheten i nämnda ett parhandel begär och Budpriset för den andra säkerheten i nämnda ett parhandelsförfrågan uppfyller en spridningsgräns bestämmer att en mängd av den andra säkerheten som kan säljas baserat på en budstorlek som är associerad med den andra säkerheten beräknar en ekvivalent mängd av nämnda första säkerhet som kan köpas Baserat på mängden av nämnda andra säkerhet som kan säljas justerar den ekvivalenta mängden av den första säkerheten baserat på justeringskriterier beräknar ett inköpspris för den justerade ekvivalenta mängden av den första säkerheten baserat på spridningsgränsen exekverar en initierande ordning för att köpa nämnda justerade ekvivalent mängd av nämnda första säkerhet till nämnda köpeskilling och utför en täckningsorder för att sälja nämnda mängd av den andra säkerheten.28 The system enligt krav 27, varvid parhandelsmotorn utför en täckningsordning för att sälja nämnda mängd av den andra säkerheten vid anbudspriset för den andra säkerheten.29 Systemet enligt krav 27, varvid parhandelsmotorn bestämmer huruvida askpriset för den första säkerheten och askpriset för den andra säkerheten uppfyller en spridningsgräns bestämmer att ett belopp av den första säkerheten som kan köpas baserat på en erbjudandestorlek i samband med den första säkerheten beräknar en motsvarande mängd av nämnda andra säkerhet som kan säljas baserat på mängden Den andra säkerheten som kan köpas anpassar nämnda ekvivalenta mängd av nämnda andra säkerhet baserat på justeringskriterier beräknar ett försäljningspris för nämnda justerade ekvivalenta mängd av nämnda andra säkerhet baserat på spridningsgränsen utförs en initierande ordning för att sälja den justerade ekvivalenta mängden av nämnda andra säkerhet till nämnda försäljningspris och utför en täckningsorder för att köpa nämnda belopp av den första säkerheten.30 Systemet med fordran 29 varvid parhandelsmotorn exekverar en täckningsorder för att inköpa nämnda mängd av den första säkerheten vid askpriset för den första säkerheten.31 Systemet enligt krav 27, varvid justeringskriterierna innefattar en minimibelopp och en maximal mängd.32 Systemet med krav 31, varvid parhandelsmotorn rundar nämnda initierande ordning till en rund lotstorlek.33. System enligt patentkrav 24, varvid parhandelsmotorn exekverar åtminstone en del av handeln med ett av nämnda värdepapper i en av nämnda parhandelstillägg i en Multipla trancher.34. System enligt patentkrav 24, varvid nämnda begäran om en parhandel har en första spridningsgräns och den andra spridningsbegäran har en andra spridningsgräns och där par-kryssnätet bestämmer att ett intervall av nämnda första spridningsgräns och nämnda andra spridningsgränser överlappar med en marknadsspridningssats ett spridningsnivå beräknar priserna för den första säkerheten och den andra säkerheten som ligger inom marknaden spridas och baseras på nämnda spridningsnivå och matc Hes nämnda andra delen av handeln med nämnda första säkerhet i nämnda begäran om ett parhandel och åtminstone en första del av handeln med den andra säkerheten i nämnda begäran om ett parhandelsförfrågan mot en annan av nämnda flertal förfrågningar om parhandel baserat på de beräknade priserna .35 System enligt patentkrav 34, varvid parkorsningsnätet beräknar ett medelvärde mellan nämnda första spridningsgräns och nämnda andra spridningsgräns och sätter nämnda spridningsnivå som nämnda menar om nämnda medelvärde ligger inom nämnda marknadsspridning.36. System enligt krav 35, varvid parkorsnätet identifierar ett spridningsbelopp som ligger närmast nämnda medelvärde och inom nämnda marknadsspridning och sätter nämnda spridningsnivå som nämnda spridningsbelopp om nämnda medel inte ligger inom nämnda marknadsspridning.37 Systemet enligt patentkrav 24, varvid nämnda ettparhandelskrav har En första spridningsgräns, ett köpförhållande och ett försäljningsförhållande, nämnda andra handelsförfrågan har en andra spridningsgräns, ett inköpsförhållande och ett försäljningsförhållande och varvid parkorsöverföringsnätet bestämmer att s biståndsförhållandekvot och nämnda försäljningsförhållande som är associerat med nämnda ett parhandelskrav, motsvarar inte nämnda köpförhållande och nämnda försäljningsförhållande för nämnda andra parhandelstillägg och att en överlappning existerar mellan intervallet av nämnda första spridningsgräns och den andra spridningsgränsen och en marknadsspridning bestämmer att marknadspriserna existerar inom överlappningen bestämmer ett felmatchningsbelopp i den andra säkerheten baserat på en skillnad mellan nämnda köpförhållande och försäljningsförhållandet som är associerat med nämnda ett parhandelsförfrågan och nämnda köpförhållande och nämnda försäljningsförhållande för den andra Parhandelsförfrågan beräknar en korsmängd för nämnda första säkerhet och nämnda andra säkerhet väljer ett korsningspris för nämnda första säkerhet och nämnda andra säkerhet som ligger inom nämnda överlappning bestämmer att nämnda felaktiga mängd är tillgänglig vid nämnda korsningspris för nämnda andra säkerhetskampanjer nämnda andra Del av handeln hos den första säkerheten i nämnda handelsförfrågan och åtminstone nämnda första del av handeln Av nämnda andra säkerhet i nämnda 1-par-handelsförfrågan mot nämnda andra par-handelsförfrågan baserad på nämnda valda priser och utför en transaktion för nämnda icke-matchande mängd av nämnda andra säkerhet vid nämnda övergångspris för nämnda andra säkerhet. 38. System enligt patentkrav 37, varvid Parkorsöverföringsnätet bestämmer att nämnda felaktiga mängd är tillgängligt på en extern marknad vid nämnda korsningspris för nämnda andra säkerhet.39. System enligt patentkrav 37, varvid parkorsöverföringsnätet bestämmer att nämnda felaktiga mängd är tillgänglig vid nämnda korsningspris för nämnda andra säkerhet i Sade en orderinventering av en finansiell institution.40 Systemet enligt patentkrav 24, varvid nämnda ett parhandelsförfrågan och nämnda andra parhandelstillägg indikerar ett antal spridningar och varvid parkorsnätverket matchar nämnda andra del av handeln hos nämnda första säkerhet i Nämnda ett par handelsförfrågan och åtminstone nämnda första del av handeln med den andra säkerheten i nämnda ett parhandel kräver t mot nämnda andra parhandelsförfrågan om nämnda antal spridningar är större än ett minimalt antal spreads.41. Systemet enligt patentkrav 24, varvid nämnda flertal parhandelstillägg innefattar åtminstone några parhandelstillägg som indikerar en preferens för exekvering via nämnda parövergång Nätverket, vilket system vidare innefattar en portföljhanterare i kommunikationen med nämnda parövergångsnätverk, varvid portföljhanteraren mottar nämnda flertal parhandelstillägg och dirigerar nämnda åtminstone några av nämnda flertal handelsförfrågningar till nämnda parövergångsnätverk enligt nämnda preferens.42 24. System enligt patentkrav 24, vilket system vidare innefattar en parhandelsmotor för att utföra åtminstone en del av nämnda flertal parhandelstillägg, varvid systemet vidare innefattar en portföljförvaltare i kommunikation med nämnda parhandelsmotor, varvid nämnda flertal parhandelskrav innefattar att Minst några parhandelstillägg som indikerar en preferens för utförande via nämnda parhandelsmotor, Nämnda portföljförvaltare mottager nämnda antal parhandelstillägg och dirigerar nämnda åtminstone några av nämnda flertal handelsförfrågningar till nämnda parhandelsmotor enligt nämnda preferens.43. Förfarande enligt krav 24, varvid en klient skickar en fråga angående en status hos nämnda par handelsförfrågan och statusen för nämnda parhandelskrav uppdateras kontinuerligt i realtid.44. Förfarande enligt krav 41, varvid preferensen är inlämnad av en klient elektroniskt.45. Förfarande enligt krav 24, varvid en klient mottar en simultan rapport när paret handlar Förfrågan fylls och klienten bekräftar nämnda parhandel elektroniskt.46 Ett datorläsbart lagringsmedium som lagrar instruktioner för att uppfylla en parhandelskrav som, när den exekveras av en dator, medför att datorn ska ta emot ett flertal parhandelstillägg, innefattande ett par handelsförfrågan och ett annat parhandelskrav, varvid varje parhandelstillägg innefattar en begäran om handel med en första säkerhet, en förfrågan att handla en se cond säkerhet och en begäran att handla den första säkerheten och den andra säkerheten med en minsta spridningsgräns och varvid den första säkerheten och den andra säkerheten vardera har ett budpris och ett askpris. bestämmer budsbudet spridda på marknaden av nämnda första säkerheten och den andra säkerheten. determin frågar fråga spridas på marknaden för den första säkerheten och den andra säkerheten. bestämmer att minsta spridningsgränsen för varje parhandelsförfrågan är uppfylld av ett antal budbudsfördelningar och nämnda fråga fråga spridningen. exekvera en transaktion mellan en första del av handeln med den första säkerheten i nämnda begäran om ett parhandel och åtminstone en begäran om icke-parhandel, under förutsättning att minsta spridningsgränsen för nämnda begäran om ett parhandel är uppfylld av intervallet av nämnda Budbudet sprids och sagda fråga fråga spridning och matcha en andra del av nämnda handel med nämnda första säkerhet i nämnda begäran om ett parhandel och åtminstone en första del av handeln med den andra säkerheten i nämnda parhandel Förutsatt att ett intervall av minsta spridningsgränsen för nämnda begäran om ett parhandelsförfrågan och nämnda andra handelsförfrågning överlappar varandra med nämnda intervall av budspridningspridningen och nämnda frågespridningsfördelning. KROSS REFERENCE TO RELATED APPLICATION. Denna ansökan hävdar förmånen för inlämningsdagen för den amerikanska provisoriska ansökan Ser nr 60 334 163 med titeln Method and System for Trading Pairs of Securities, som inlämnades den 29 november 2001, vars innehåll införlivas som referens häri. Avser ett system och en metod för handel med värdepapper och i synnerhet för ett system och en metod för handel med värdepapper i par. En redovisad strategi för handel med värdepapper kallas parhandel. Parhandel är en icke-riktad investeringsstrategi där investerare identifierar två värdepapper med liknande egenskaper och värdepapperen handlar för närvarande vid ett prisförhållande som ligger utanför deras historiska handelsområde Investerare utnyttjar prisförhållandet mellan värdepapperen genom att köpa den undervärderade säkerheten samtidigt som den säljer den övervärderade säkerheten. Eftersom parhandel är en marknadsneutral strategi är det en särskilt önskvärd strategi att investera i volatila marknader. Ett sammanhang där parhandel är användbart är där en investerare vill utnyttja en arbitrage möjlighet till följd av en sammanslagning mellan två företag. Till exempel har bolag A meddelat ett slutgiltigt avtal om förvärv av bolag T, i vilket fall bolagets aktieägare kommer att få 0 5 aktier av bolag A Varje aktie av bolagets T-aktie de äger Investeraren önskar fånga spridningen mellan den erbjudna ersättningen 0 5 A-aktier och priset på T-aktien För att göra detta köper investeraren aktier i T-lager och säljer aktier i A-lager. För exempel om aktie T handlas till 28 per aktie och aktie A handlas till 60 per aktie, kan investeraren genomföra en handel för 200 000 spreadar genom att köpa 200 000 s har T-aktier och säljer 100 000 aktier i A-aktien Efter samgåendet äger investeraren täckning av den korta positionen i lager A med de 100 000 aktierna i A-aktien som investerarna erhåller i utbyte mot de 200 000 aktier som investeraren innehade av lager T Genom att utföra parhandeln låser investeraren en vinst på 400 000, förutsatt att fusionen går igenom. Processen att utföra ett parhandel innefattar således exekvering av enskilda branscher riktade mot varje ben i parhandelens begäran. Ett exempel på ett system för att utföra handel för Att fylla i ett parhandelsförfrågan är Quantex-systemet från ITG på 380 Madison Avenue New York, NY 10017. En utmaning när det gäller att implementera ett parhandel är att hitta en motpart för en viss position som en investerare vill etablera samtidigt som risken för benet sätts. parhandel utförs utanför marknaden som en privat transaktion som förhandlas av ett finansiellt institut som tjänar stora kunder. Om en investerare exempelvis vill utföra en Air trade betting som en föreslagen fusion mellan två företag kommer att gå igenom, skulle investeraren närma sig ett finansiellt institut som söker en investerare som är villig att satsa mot fusionen. Finansinstitutet fungerar då som mellanhand mellan de två investerarna där investerarna etablerar lika och motsatta positioner i de föreslagna fusionspartnernas lager och därigenom fullbordar parhandeln. Således genom att matcha tvåparsförfrågningar så att transaktionerna som är förknippade med var och en av parhandelens ben utförs samtidigt, är ingen investerare utsatt för benrisk som annars skulle resultera för tidsperioden mellan utförandet av det första benet och det andra benet i parhandeln. Det finns många nackdelar i samband med den vanliga parhandeln. För det första är parhandel vanligtvis begränsad till kunder i stora finansiella institutioner som har förmågan Att identifiera lämpliga motparter för ett visst parhandel Detta är speciellt fallet whe n Parhandeln innebär en stor mängd aktier eller illikvida bestånd där det enda sättet att utföra handeln och minimera benrisken är via en marknadsförmedling som förhandlas av ett finansiellt institut. Eftersom en parhandel ofta förhandlas fram av parterna med ett finansiellt institut som mellanhand är processen ofta långsam och ineffektiv. Parhandel enligt nuvarande praxis är i allmänhet bäst lämpad för stora kunder som vill etablera stora positioner och därigenom ge finansinstituten det ekonomiska incitamentet att genomföra transaktionen Mindre Klienter måste dock förlita sig på marknaderna för genomförande av parhandel, vilket är olämpligt för illikvida bestånd och leder också till ökad benrisk. Följaktligen är det önskvärt att tillhandahålla ett system och en metod för handel med värdepapper i par. Sammanfattning av uppfinningen. Föreliggande uppfinning avser att övervinna nackdelarna med de tidigare kända parhandelskraven. Enligt föreliggande uppfinning a Metoden tillhandahålls för att uppfylla en parhandelförfrågan och innefattar stegen att mottaga ett flertal parhandelstillägg, som utför en transaktion för en första del av en av flera parhandelstillägg och matchar en andra del av den ena av flertalet par handelsförfrågningar mot en annan av flertalet förfrågningar om parhandel. I en exemplifierande utföringsform innefattar metoden steget att exekvera en transaktion för en första del av en av flera parhandelstillägg på en extern marknad. I en annan exemplifierande utföringsform Metoden innefattar steget att exekvera en transaktion för en första del av en av de flera parhandelskraven mot orderinventeringen. I ännu en exemplifierande utföringsform innefattar parhandelskravet en första säkerhet som har ett budpris och ett askpris och ett den andra säkerheten har ett budpris och ett askpris, och metoden innefattar stegen att bestämma om budpriset för den första säkerheten och budet pr ice of the second security meet a spread limit determining an amount of the second security that can be sold based on a bid size associated with the second security calculating an equivalent amount of the first security that can be bought based on the amount of the second security that can be sold adjusting the equivalent amount of the first security based on adjustment criteria calculating a purchase price for the adjusted equivalent amount of the first security based on the spread limit executing an initiating order to buy the adjusted equivalent amount of the first security at the purchase price and executing a covering order to sell the amount of the second security. In still yet another exemplary embodiment, the method includes the step of executing a covering order to sell the amount of the second security at the bid price of the second security. In an exemplary embodiment, the method includes the steps of determining whether the ask price of the first security and the ask price of the second security and or the bid price of the first security and the bid price of the second security meet a spread limit determining an amount of the first security that can be bought based on an offer size associated with the first security calculating an equivalent amount of the second security that can be sold based on the amount of the second security that can be bought adjusting the equivalent amount of the second security based on adjustment criteria calculating a selling price for the adjusted equivalent amount of the second security based on the spread limit executing an initiating order to sell the adjusted equivalent amount of the second security at the selling price and executing a covering order to purchase the amount of the first security. In another exemplary embodiment, the method includes the step of executing a covering order to purchase the amount of the first security at the ask price of the first security. In yet another exemplary embodiment, the adjustment criter ia include a minimum amount and a maximum amount. In still yet another exemplary embodiment, the method includes the step of rounding the initiating order to a round lot size. In an exemplary embodiment, the method includes the step of executing a first portion of one of the plurality of pair trade requests in a plurality of tranches. In another exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit and the another of said plurality of trade requests has a second spread limit and wherein the method includes the steps of determining that a range of the first spread limit and the second spread limit overlaps with a market spread setting a spread level calculating prices for the first security and the second security that are within the market spread and based on the spread level and matching the second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests based on the calculated prices. In yet another exemplary embodiment, the method includes the steps of calculating a mean between the first spread limit and the second spread limit and setting the spread level as the mean if the mean is within the market spread. In still yet another exemplary embodiment, the method includes the step of identifying a spread amount that is closest to the mean and within the market spread and setting the spread level as the spread amount if the mean is not within the market spread. In an exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit, a buy ratio and a sell ratio, the another of the plurality of trade requests has a second spread limit, a buy ratio and a sell ratio and the method includes the steps of determining that the buy ratio and the sell ratio associated with the one of the plurality of trade requests does not equal the buy ratio and the sell ratio of the another of the plurality of trade requests and that an overlap exists between range of the first spread limit and the second spread limit and a market spread determining that market prices exist that are within the overlap determining a mismatch amount in the second security based on a difference between the buy ratio and the sell ratio associated with the one of the plurality of trade requests and the buy ratio and the sell ratio of the another of the plurality of trade requests calculating a cross amount for the first security and the second security selecting a crossing price for the first security and the second security that is within the overlap determining that the mismatch amount is available at the crossing price for the second security matching the second portio n of the one of the plurality of pair trade requests against another of the plurality of pair trade requests based on the calculated prices and executing a transaction for the mismatch amount of the second security at the crossing price for the second security. In another exemplary embodiment, the method includes the step of determining that the mismatch amount is available in an external market at the crossing price for the second security. In yet another exemplary embodiment, the method is performed by a financial institution having order inventory and includes the step of determining that the mismatch amount is available in the order inventory at the crossing price for the second security. In still yet another exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests indicate a number of spreads and the method includes the step of matching a second portion of the one of the plurality of pair trade requests against anot her of the plurality of pair trade requests if the number of spreads is greater than a minimum number of spreads. In an exemplary embodiment, the method includes the step of receiving a preference for filling at least some of the plurality of trade requests via the step of executing a transaction for a first portion of one of the plurality of pair trade requests, described above. In another exemplary embodiment, the method includes the step of receiving a preference for filling at least some of the plurality of trade requests via the step of matching a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests, described above. Under the present invention, a method for fulfilling a pair trade request is provided and includes the steps of receiving a plurality of pair trade requests and matching at least a portion of one of the plurality of pair trade requests against another of the plurality of pair trade requests. Under the pr esent invention, a system for fulfilling a pair trade request is provided, the system receiving a plurality of pair trade requests and includes a pair trading engine for executing a transaction for a first portion of one of the plurality of pair trade requests The system also includes a pair crossing network for matching a second portion of said one of the plurality of pair trade requests against another of the plurality of pair trade requests. In an exemplary embodiment, the system includes a link to external markets and wherein the pair trading engine executes the transaction for the first portion of one of the plurality of pair trade requests in the external markets. In another exemplary embodiment, the system includes a financial institution having an order inventory and wherein the pair trading engine executes the transaction for the first portion of one of the plurality of pair trade requests against the order inventory. In yet another exemplary embodiment, the pair trade request in cludes a first security having a bid price and an ask price and a second security having a bid price and an ask price, and wherein the pair trading engine determines whether the bid price of the first security and the bid price of the second security meet a spread limit determines an amount of the second security that can be sold based on a bid size associated with the second security calculates an equivalent amount of the first security that can be bought based on the amount of the second security that can be sold adjusts the equivalent amount of the first security based on adjustment criteria calculates a purchase price for the adjusted equivalent amount of the first security based on the spread limit executes an initiating order to buy said adjusted equivalent amount of the first security at the purchase price and executes a covering order to sell the amount of the second security. In still yet another exemplary embodiment, the pair trading engine executes a covering order to sell th e amount of the second security at the bid price of the second security. In an exemplary embodiment, the pair trading engine determines whether the ask price of the first security and the ask price of the second security meet a spread limit determines an amount of the first security that can be bought based on an offer size associated with the first security calculates an equivalent amount of the second security that can be sold based on the amount of the second security that can be bought adjusts said equivalent amount of the second security based on adjustment criteria calculates a selling price for the adjusted equivalent amount of the second security based on the spread limit executes an initiating order to sell the adjusted equivalent amount of the second security at the selling price and executes a covering order to purchase the amount of the first security. In another exemplary embodiment, the pair trading engine executes a covering order to purchase the amount of the first securi ty at the ask price of the first security. In yet another exemplary embodiment, the pair trading engine rounds the initiating order to a round lot size. In still yet another exemplary embodiment, the pair trading engine executes a first portion of one of the plurality of pair trade requests in a plurality of tranches. In an exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit and the another of the plurality of trade requests has a second spread limit and wherein the pair crossing network determines that a range of the first spread limit and the second spread limit overlaps with a market spread sets a spread level calculates prices for the first security and the second security that are within the market spread and based on the spread level and matches the second portion of said one of the pluralit y of pair trade requests against another of the plurality of pair trade requests based on the calculated prices. In another exemplary embodiment, the pair crossing network calculates a mean between the first spread limit and the second spread limit and sets the spread level as the mean if the mean is within the market spread. In yet another exemplary embodiment, the pair crossing network identifies a spread amount that is closest to the mean and within the market spread and sets the spread level as the spread amount if the mean is not within the market spread. In still yet another exemplary embodiment, the one of said plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit, a buy ratio and a sell ratio, the another of the plurality of trade requests has a second spread limit, a buy ratio and a sell ratio and wherein the pair crossing net work determines that the buy ratio and the sell ratio associated with the one of the plurality of trade requests does not equal the buy ratio and the sell ratio of the another of the plurality of trade requests and that an overlap exists between range of the first spread limit and the second spread limit and a market spread determines that market prices exist that are within the overlap determines a mismatch amount in the second security based on a difference between the buy ratio and the sell ratio associated with the one of the plurality of trade requests and the buy ratio and the sell ratio of the another of the plurality of trade requests calculates a cross amount for the first security and the second security selects a crossing price for the first security and the second security that is within said overlap determines that the mismatch amount is available at the crossing price for the second security matches the second portion of the one of the plurality of pair trade requests aga inst another of the plurality of pair trade requests based on the calculated prices and executes a transaction for the mismatch amount of the second security at the crossing price for the second security. In an exemplary embodiment, the pair crossing network determines that the mismatch amount is available in an external market at the crossing price for the second security. In another exemplary embodiment, the pair crossing network determines that the mismatch amount is available in the order inventory at the crossing price for the second security. In yet another exemplary embodiment, the one of said plurality of pair trade requests and the another of the plurality of pair trade requests indicate a number of spreads and wherein the pair crossing network matches a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests if the number of spreads is greater than a minimum number of spreads. In still yet another exemplary embodim ent, the plurality of pair trade requests include at least some pair trade requests indicating a preference for execution via said pair crossing network, and the system further includes a portfolio manager in communications with the pair crossing network, the portfolio manager receiving the plurality of pair trade requests and routing the at least some pair trade requests to the pair crossing network according to the preference. In an exemplary embodiment, the system includes a pair trading engine for executing at least some of the plurality of pair trade requests, further includes a portfolio manager in communications with the pair trading engine and wherein the plurality of pair trade requests include at least some pair trade requests indicating a preference for execution via the pair trading engine, the portfolio manager receiving the plurality of pair trade requests and routing the at least some of the plurality of trade requests to the pair trading engine according to the preferenc e. Under the present invention, a system for fulfilling a pair trade request is provided, wherein the system receives a plurality of pair trade requests and includes a pair crossing network for matching at least one of the plurality of pair trade requests against another of the plurality of pair trade requests. Accordingly, a method and a system are provided for trading pair securities. The invention accordingly comprises the features of construction, combination of elements and arrangement of parts that will be exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims Other features and advantages of the invention will be apparent from the description, the drawings and the claims. DESCRIPTION OF THE DRAWINGS. For a fuller understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawings, in which. FIG 1 is a block diagram of a system for trading securities in pairs accordi ng to the present invention. FIG 2 is a flowchart of the steps a pair trading engine included in the system of FIG 1 applies to fill a pair trade request. FIG 3 is a flowchart of the steps a pair crossing network included in the system of FIG 1 applies to fill a pair trade request. FIG 4 is a flowchart of a process by which the pair crossing network of the system of FIG 1 fills imperfectly matched orders and. FIG 5 is a graph for identifying the market prices for two securities that meet the required spread limits. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS. Referring now to FIG 1 there is shown a block diagram of a system 1 for trading securities in pairs according to the present invention System 1 receives pair trade requests from clients operating client access devices 7 and attempts to fill the pair trade requests according to the parameters associated with the particular pair trade request System 1 includes two different subsystems for filling pair trade requests a pair trading e ngine 3 and a pair crossing network 5 As will be described below, pair trading engine 3 receives a pair trade request and attempts to fill in whole or in part the trade request by executing the appropriate trades in an external market 13 that may include, by way of non-limiting example, the New York Stock Exchange, the NASDAQ or any other financial market Pair trading engine 3 may also fill in whole or in part a pair trade request by executing a transaction against order inventory 11 of non-pair trade requests controlled by the financial institution that is operating system 1 In addition, pair trading engine may also fill in whole or in part a pair trade request by forwarding the trade request to pair crossing network 5 for matching with other pair trade requests. Likewise, pair crossing network 5 receives a pair trade request and fulfills in whole or in part the request by matching it against another pair trade request received by pair crossing network 5 by matching the request against inventory 11 controlled by the financial institution and or by forwarding the trade request to pair trading engine 3 for execution in external markets 13.System 1 also includes a portfolio manager 9 that may be, for example, a software program executing on a computer system that receives the pair trade requests from client access device 7 and presents the trade request to either pair trading engine 3 pair crossing network 5 or both, depending on the trade parameters set by the client Also, the client may query portfolio manager 9 regarding the status of any pair trade request the client has presented to system 1.In operation, system 1 may fulfill a pair trade request either using pair trading engine 3 or pair crossing network 5 or a combination of the two For example, a pair trade request received by system 1 may be completely filled by pair trading engine 3 as follows. Assume a case where XYZ is taking over ABC and is offering 0 575 shares of XYZ for each ABC share and investor Arb wa nts to invest in the price difference between ABC stock and XYZ stock To take advantage of the price difference, Arb wants to lock in the difference between the value offered 0 575 XYZ stock and the value of ABC stock by buying ABC stock and selling XYZ stock subject to the condition that ABC 0 575 XYZ 1 19 i e Arb desires to capture a 1 19 difference between XYZ s takeover offer and ABC s share price. In order to fill this pair trade, Arb presents a pair trade request to portfolio manager 9 using client access device 7 The pair trade request typically includes a number of parameters that define the pair trade and that also may be used by portfolio manager 9 in determining how the pair trade request is to be filled Arb typically indicates in the trade request the number of spreads the Arb desires to invest in and also provides a minimum and maximum share amount that he is willing to trade per tranche. For example, Arb may indicate a desire to invest in 100,000 spreads and may only wish t o trade the spread 3,000-8,000 shares at a time Arb generally sets this tranche size range based on the liquidity and volatility of ABC stock and XYZ stock Arb may set a larger minimum tranche size if ABC stock and XYZ stock are fairly liquid stocks because higher liquidity increases the likelihood that a larger tranche size will be executed Arb may set a lower maximum tranche size if XYZ stock and ABC stock are volatile stocks so as to limit the leg risk associated with executing a pair trade. Yet another pair trade parameter Arb provides is the spread limit in the above case 1 19 which is the amount Arb desires to capture in the trade Arb does not have to provide, however, the discrete prices at which trades for ABC and XYZ stock are to be executed as these prices are calculated by pair trading engine 3 and or pair crossing network 5 , as will be described below. Referring now to FIG 2 there is shown a flowchart describing the steps pair trading engine 3 applies to fill a pair trade re quest The flowchart in FIG 2 is based on the above example and the market data listed in Table 1 below. Initially, in Step 201 pair trading engine 3 determines whether the bid bid prices or ask ask prices of ABC and XYZ stock, respectively, meet the spread limit requirement of the particular pair trade request In this case the bid bid spread is 1 4375 122 50 0 575 69 and the ask ask spread is 1 1969 122 625 0 575 69 3125 so that each spread is less than the spread limit of 1 19, as is required for this particular trade Once it is determined that either the bid bid spread or the ask ask spread meets the spread limit, then in Step 202 it is determined as is indicated in Table 1 how much XYZ stock can be sold at the bid and how much ABC stock can be bought at the ask In an exemplary embodiment, the client may specify whether the bid bid spread, the ask ask spread or either the bid bid or the ask ask spread must exceed the indicated spread limit for a transaction to proceed If neither the b id bid spread nor the ask ask spread meets the spread limit, the process waits a period of time for example 0 10 seconds and returns to Step 201 to again test whether the bid bid spread or the ask ask spread meets the spread limit. Next, in step 203 an equivalent amount of stock that can be sent into the market i e bought sold in the market is calculated for a spread based on the bid bid price spread and or the ask ask price spread that meets the spread limit In this example, if a maximum of 10,000 shares of XYZ stock can be sold into the market i e the XYZ bid size then, based on the ABC XYZ ratio of 1 0 575 in this case , a total of 17,391 10,000 0 575 shares of ABC stock are to be bought in order to execute a balanced pair trade Likewise, if a maximum of 1,500 shares of ABC stock can be bought in the market i e the ABC ask size , then, based on the ABC XYZ ratio of 1 0 575 in this case , a total of 863 1500 0 575 shares of XYZ stock are to be sold in order to execute a balanced pair trade. Next, in Step 204 the pair trade share amounts calculated in Step 203 are adjusted to conform to the wave maximum and minimum parameters i e the maximum minimum tranche size included in the pair trade request as well as market round lot limits In the above example, the amount of ABC shares to be bought that was calculated based on the XYZ bid size i e 17,391 is first rounded to an even lot size i e 17,400 and then reduced to the maximum tranche size of 8000 Also, the amount of XYZ shares to be offered that was calculated based on the ABC ask size i e 863 is first rounded to an even lot size i e 900 and then increased to 1,700 shares to meet the minimum tranche size of 3000 3000 0 575 1777 In an exemplary embodiment the minimum and maximum tranche size is scaled by the particular ratio for example, in the above case, the tranche sizes for XYZ stock is scaled by 0 575 In another embodiment, the maximum minimum tranche size is used for each security in the pair trade request without scaling In yet another exemplary embodiment, the pair trade request includes a separate maximum minimum tranche for each security. Once the share amounts for the pair trade are calculated, in Step 205 the share prices that are needed to meet the spread limit of the pair trade request are calculated For example, for a pair trade based on the bid bid price spread, in order to meet the spread limit of 1 19 credit, the price at which ABC stock is to be bid should be no greater than 69 2475 122 50 0 575 1 19 a share Likewise, for a pair trade based on the ask ask price spread, in order to meet the spread limit, the price at which XYZ stock is to be offered should be greater than or equal to 122 6130 69 3125 1 19 0 575 a share. Next, once the pair trade share amounts and share prices have been calculated, in Step 206 pair trading engine 3 sends initiating orders to external markets 13 in order to fill the pair trade request The initiating orders may include an initiating order for executing a pair trade based on the bid bid spread in this case a bid for 8,000 shares of ABC stock at 69 2475 and or an initiating order for executing a pair trade based on the ask ask spread in this case an offer of 1,700 shares of XYZ stock at 122 6130.Finally, as the initiating orders sent to external markets 13 in Step 207 get filled, pair trading engine 3 automatically sends into the market the covering side of the pair trade So, for example, as the initiating order of buying 8,000 shares of ABC stock at 69 2475 gets filled, pair trading engine 3 sends an order to external markets 13 to sell 4,600 8,000 0 575 shares of XYZ stock at 122 50.In an exemplary embodiment, the client s pair trade request includes threshold amounts that indicate the amount of variance in stock price and or share amount the client is willing to absorb For example, if in the process of covering the initiating order the price of XYZ stock dips to 122 49 in which case the spread limit of the pair trade would drop to 1 18 , then pair trading engine 3 would still sell XYZ stock at the price of 122 49 if the 0 01 difference was within the threshold amount included in the pair trade request Similarly, the pair trade request may include threshold amounts for any other pair trade parameter, including by way of non-limiting example, the number of spreads to be purchased and the tranche sizes If, however, a particular threshold amount indicated by the client is exceeded for any given pair trade parameter, then pair trading engine 3 would attempt to cancel the initiating order and or the covering order that may be possible if the orders have not yet reached the market or have not yet been filled In such a case, pair trading engine 3 would then repeat the above analysis for determining suitable initiating and cover orders. To fill a pair trade request, pair trading engine 3 executes trades utilizing the method described above Typically, pair trading engine 3 tranches a pair trade request and trades piece-meal in external markets 13 In certain cases, however, it may be difficult to fill a trade request by executing several transactions in external markets 13 either because the pair trade request is for a very large number of spreads or includes stocks that are illiquid in which cases pair trading engine 3 may be ineffective in filling the pair trade request Also, in certain situations, a client wishing to remain anonymous may indicate in the pair trade request a preference that no orders be sent to external markets 13 In these circumstances, portfolio manager 9 may route the particular pair trade request to pair crossing network 5.Referring now to FIG 3 there is shown a flowchart illustrating the steps pair crossing network 5 applies to fill a pair trade request The flowchart in FIG 3 is based on the above example and the market data listed in Table 2 below. Spread Limit as defined by 0 575 XYZ - ABC. Continuing the previous example, assume the pair trade request issued by Arb for 100,000 spreads was half-filled by pair trading engine 3 Also, assume that system 1 receives a pair trade request from Antiarb that indicates a desire to sell 30,000 shares of ABC and buy 17,200 shares a ratio of 1 0 575 and also indicates a spread limit of 1 30 i e ABC 0 575XYZ 1 30 In this case Arb and Antiarb s orders are complimentary in the primary order elements securities, ratios and buy versus sell Also, Antiarb is willing to pay 0 11 per spread more than Arb is demanding from the marketplace Based on these parameters, there is an opportunity for Arb s and Antiarb s trade requests to be filled via pair crossing network 5.If Antiarb s pair trade request was marked for trading by pair trading engine 3 then portfolio manager 9 sends Antiarb s order to pair trading engine 3 for execution Pair trading engine 3 then sends the parameters of Antiarb s trade reques t, as well as all orders waiting for execution in pair trading engine 3 to pair crossing network 5 Pair crossing network 5 will recognize as described above that there is a crossing opportunity between Arb s order and Antiarb s order In this case, pair crossing network 5 then directs pair trading engine 3 to suspend the execution of Antiarb s order in the amount that can be crossed by pair crossing network 5 30,000 spreads in this case In addition, pair trading engine 3 routes a cross amount of 30,000 spreads from Arb s order to pair crossing network 5 for crossing against Antiarb s order At this point, the pair crossing network 5 crosses the Antiarb order against a portion of Arb s order, as follows. Assume the prevailing market conditions at the time of the cross are as shown in Table 3 Furthermore, Table 3 indicates the XYZ Ratio-Adjusted Value for both the bid and ask prices based on the conversion ratio of 1 0 575 Based on the XYZ Ratio-Adjusted Values, a Bid Ask Spread Range i e t he spread provided for a cross between the bid price of ABC stock and the XYZ Ratio-Adjusted ask price of 1 3863 is calculated and an Ask Bid Spread Range i e the spread provided for a cross between the ask price of ABC stock and the XYZ Ratio-Adjusted bid price of 1 05 is calculated. To perform the cross, in Step 301 pair crossing network 5 first determines whether the range of spread limits associated with Arb s and Antiarb s trade requests i e 1 30- 1 19 coincides with the range of the prevailing market spread 1 3863- 1 05 In this example, the range of spread limits does coincide with the prevailing market spread because at least a portion of the spread limit range overlaps with a portion of the market spread Thus, a cross can occur. Next, in Step 302 pair crossing network 5 calculates the mean of Arb s and Antiarb s spread order limit which is 1 30 1 19 2 1 245 and determines whether the mean is within the range of the market spread i e 1 3863- 1 05 If it is, then in Step 303 pair cr ossing network 5 calculates the prices at which to cross The prices must be within the current markets for ABC stock and XYZ stock, and satisfy market uptick requirements for short sales , and provide a spread that is equal to the spread level calculated above For example, with the inside market for ABC stock at 70 00-70 25 and the inside market for XYZ stock at 124 00-124 15, a cross price of 70 11 for ABC stock and 124 096 for XYZ stock provides the spread of 1 2452 thereby meeting the requirement of both Arb s and Antiarb s trade request Finally, in Step 304 pair crossing network 5 crosses 30,000 shares of ABC stock at 70 11 with Arb buying and Antiarb selling and 17,200 shares of XYZ at 124 096 with Arb selling and Antiarb buying. If it is determined in Step 302 that the mean of Arb s and Antiarb s spread order limits does not fall within the range of the market spread, then in Step 305 the spread closest to the mean of the two spread limits that is also within the market spread is calculated For example, if the market spread is 1 3863- 1 28, then the mean of the two spread limits 1 245 is not within the market spread In such a case, 1 28 is selected as the spread level that is closest to the mean and within the market spread In an exemplary embodiment, the spread level at which Arb and Antiarb cross can be determined in any other suitable manner as long as the spread level is within the market spread and within the range of spread limits indicated in the pair trade requests. Once the spread level is determined, the method proceeds to Step 303 in which pair crossing network 5 calculates prices to cross at that are within the current markets for ABC stock and XYZ stock and that meet the calculated spread level In the case where the calculated spread level is 1 28, the cross will occur at a price of 70 08 for ABC stock and 124 1043 for XYZ stock Finally, the method proceeds to Step 304 in which pair crossing network 5 performs the cross between Arb and Antiarb. Once a pair trade request is filled or partially filled , the transaction details are reported to portfolio manager 9 and made available to the client operating client access device 7.In the previous example, pair crossing network 5 crosses orders in which both Arb and Antiarb desire to trade the same pair of securities in the same ratio In an exemplary embodiment, pair crossing network 5 executes a cross between two pair trade requests that are not perfectly matched. For example, assume that pair crossing network 5 receives the pair trade requests as shown in Table 4 Note that these two pair trade requests are imperfectly matched because each trade request uses a different ratio between ABC and XYZ stock. Arb s Spread Limit is defined by 0 575 XYZ - ABC. Antiarb s Spread Limit is defined by 0 6 XYZ - ABC. Also, assume the market in ABC and XYZ stocks at the time the pair trade requests are received by pair crossing network 5 is as described in Table 5 below. Arb s XYZ Ratio-Adjusted Value. Arb s Dollar Range. AntiArb s XYZ Ratio-Adjusted Value. AntiArb s Dollar Range. Referring now to FIG 4 there is shown a flowchart illustrating a process by which pair crossing network 5 fills these imperfectly matched order First, in Step 401 pair crossing network 5 determines whether Arb s buy security equals Antiarb s sell security and whether Arb s sell security equals Antiarb s buy security If both conditions are not met, then a cross between the two orders cannot occur If the two conditions are met, then in Step 402 it is determined whether Arb s buy ratio equals Antiarb s sell ratio and whether Arb s sell ratio equals Antiarb s buy ratio If these ratios are the same, then pair crossing network 5 procee ds to cross the two orders as described in the example above Note that for a cross to occur at this stage does not require the ratios themselves to match but rather that the ratios of the ratios match for e g a ratio of 2 3 matches a ratio of 0 667 1.If, however, the two ratios are not equal as in this case where Arb s sell ratio does not equal Antiarb s buy ratio , then in Step 403 pair crossing network determines whether there is an overlap between Arb s and Antiarb s spread limit that also falls within the bid ask market for ABC and XYZ stock To make such a determination, pair crossing network 5 calculates whether there are market prices for both ABC and XYZ stock that satisfy the following inequalities L 1 Ratio A ABC Ratio B XYZ and 1 L 2 Ratio C ABC Ratio D XYZ 2 Where L1 is Arb s spread limit of 1 19 credit, L2 is Antiarb s spread limit of 4 40 debit, RatioA is Arb s buy ratio of 1 1, RatioB is Arb s sell ratio of 1 0 575, RatioC is Antiarb s sell ratio of 1 1 and RatioD is Anti arb s buy ratio of 1 0 6.Referring now to FIG 5 there is shown a graph 51 that depicts market prices for ABC and XYZ stock that meet the spread limits of Arb and Antiarb In graph 51 the x-axis represents the prices for XYZ stock while the y-axis represents the prices for ABC stock Graph 51 includes a shaded area 53 that is the universe of market prices for ABC and XYZ stock that could satisfy the spread trade involving those stocks Also included in graph 53 is a spreadlimit line L1 inequality 1 , above that represents the spread limit associated with Arb and a spread limit line L2 inequality 2 , above that represents the spread limit associated with Antiarb Thus, the solution set of market prices that satisfies inequalities 1 and 2 is the portion of dark shared area 53 that falls between spread limit line L1 and spread limit line L2 In this example, a cross at a share price for ABC of 70 14 and a share price of 124 15 for XYZ stock meets the investor s spread limits and falls within th e market prices for ABC and XYZ stock. If it is determined that no share prices for both ABC and XYZ stock satisfy Arb s and Antiarb s spread limits, then no cross can occur If such share prices do exist, then in Step 404 it is determined which of the investors desires to transact in fewer shares of ABC stock and a mismatch in share amounts caused by the differing ratios is determined In our example, Antiarb desires to sell fewer ABC shares than Arb desires to buy 30,000 vs 50,000 Then, in Step 405 pair crossing network 5 determines the number of XYZ shares that can be crossed between Arb and Antiarb based on the maximum amount of ABC shares that can be crossed 30,000 in this example Based on the Antiarb ABC order quantity of 30,000 shares, the maximum number of XYZ shares that Arb will cross with Antiarb is.30 000 Arb XYZ Ratio Arb ABC Ratio 30 000 0 575 1 17 300 17 250 rounded to an even lotsize. While the maximum quantity of XYZ shares that Arb will cross is 17,300, Antiarb s trade re quest indicates a desire to cross 18,000 shares To overcome this imbalance, in Step 406 pair crossing network 5 is in communications with external markets 13 for determining whether the excess 700 XYZ shares needed to satisfy Antiarb s trade request can be transacted for in external markets 13 In an exemplary embodiment, pair crossing network 5 makes this determination by issuing a query to pair trading engine 3 as to whether 700 shares of XYZ stock can be bought in external markets 13 Because, as indicated in Table 5, 3,000 shares of XYZ stock are offered at 124 15, pair trading engine 3 responds to pair crossing network 5 that the 700 shares needed to balance the cross between Arb and Antiarb are available from external markets 13 at 124 15.Next, in Step 407 pair crossing network calculates the cross prices that are necessary such that Arb and Antiarb achieve their respective spread limits while also incorporating the excess 700 shares of XYZ stock that must be purchased from externa l markets 13 at 124 15 to satisfy Antiarb s trade request An example of such cross prices that meet these criteria is a price of 70 14 for ABC stock and a price of 124 15 for XYZ stock. Once the cross prices are calculated, in Step 408 pair crossing network 5 crosses 30,000 shares of ABC stock and 17,300 shares of XYZ stock between Arb and Antiarb and also buys 700 shares of XYZ stock at 124 15 in external markets 13 on behalf of Antiarb Thus, both Arb and Antiarb s pair trade requests are satisfied. Alternatively, the entire 18,000 shares of XYZ stock may be crossed thereby fully satisfying Antiarb s trade request In such a case, the ratio mismatch is addressed by Arb purchasing an additional 1200 700 0 575 rounded to a lotsize shares of ABC stock from external market 13 or from firm inventory 11.Once the trade is completed, the details of the transaction are provided to portfolio manager 9 to report the transaction details to the investors. In an exemplary embodiment, a pair order or po rtion thereof may be filled against an internal inventory 11 of trade requests maintained by the financial institution operating system 1 For example, in the previous example in which an excess of 700 shares of XYZ stock needs to be purchased in order for a match i e cross between Arb and Antiarb s trade requests to occur, instead of determining whether the 700 shares are available in external markets 3 pair crossing network 5 examines firm inventory 11 to determine whether the shares are available at the required price Likewise, in cases where pair trading engine 3 desires to execute a pair trade based on orders to be sent to external markets 13 pair trading engine 3 may first determine whether the order can be filled, in whole or in part, using trade requests pending in firm inventory 11 Generally, the advantages of filling an order using pending trade requests in firm inventory 11 is that execution is faster, transaction costs are lower and leg risk is minimized. In another exemplary embodiment, a client s pair trade request may also include a minimum number of spreads that can be traded in pair crossing network 5 Also, pair crossing network 5 may be designed to require a minimum share amount for a cross to occur A minimum number of spreads that can be traded may be provided in order to reduce the distractions and booking costs associated with numerous smaller trades that may exceed the benefits of a de minimis fill. In another exemplary embodiment, portfolio manager 9 publishes the inside cross market for any pair that a client has selected for crossing in pair crossing network 5 In still another exemplary embodiment, the client has the option for each pair trade selected for crossing in pair crossing network 5 to designate that the order should be reflected in the published inside cross market This inside cross market consists of the tightest spread bid and offer and corresponding bid size and offer size from all client pair orders pending in pair crossing networ k 5 In this way, a client can assess the likelihood and timing of a pair trade request being filled by pair crossing network 5 Also, by publishing the client s spread interest, others seeking liquidity can trade at the client s level. In an exemplary embodiment, the client can designate each pair order designated for pair trading engine 3 and or pair crossing network 5 for Broker Negotiation If Broker Negotiation is designated, the client s broker-dealer sales representative is notified of the client s spread order thereby prompting the broker-dealer to solicit a complementary, agency order from another client The client may also designate each pair order for Broker Facilitation in which case the client allows the broker-dealer to act principally to fill the client s order. In summary, the advantages to a client of using pair trading engine 3 is that pair trading engine 3 allows the client to trade a spread order while limiting leg risk or the risk of missing a targeted spread level This is accomplished by breaking the total order into tranches of sizes proportionate to the market, subject to user minimums and maximums, that can be traded in external markets 13 or against firm inventory 11 Orders executed via pair trading engine 3 however, are typically of a lower traded volume because trading is constrained to the liquidity available in the market In contrast, trades executed via pair crossing network 5 are not constrained by market liquidity and do not have to be tranched to minimize leg risk In particular, the benefits of filling a pair trade request via pair crossing network 5 are as follows. Elimination of Leg Risk Pair crossing network 5 potentially provides a deeper well of liquidity because the trades are brokered, as a spread, directly between spread investors via a central clearing facility Moreover, the introduction and use of a pair trading facility eliminates the leg risk described above without a sacrifice of liquidity. Large Transactions Only Certain larg e investors may prefer to use pair crossing network 5 rather than pair trading engine 3 to avoid having a trade request broken up into numerous small executions For example, sudden, brief moves in one of the two stocks included in the pair trade request may cause pair trading engine 3 to issue numerous small executions to fill the request While a small investor may welcome capturing these small opportunities, a large investor may find such small executions to be more of a nuisance than a service. Price Setting versus Price Taking Large investors seeking liquidity may prefer to set their price via the pair crossing network 5 Also, other spread investors looking for liquidity can use pair crossing network 5 to monitor and trade with the large investor at the large investor s level While client orders directed to pair trading engine 3 can designate a spread limit, such orders are essentially price-takers as the market reaches the desired level, the orders are executed Moreover, the pair tr ading engine tranching mechanism creates relatively small orders, allowing institutional flows to move the individual stocks As a result, the small, tranched orders generated by pair trading engine 3 can become overpowered by single-name institutional flows In addition, orders designated solely for pair trading engine 3 and not for pair crossing network 5 are not published to a central quote facility such as by portfolio manager 9 thereby preventing other spread traders from knowing the size and limit of a pair trading engine order. Illiquid Stocks vs Liquid Stocks Spreads that include one or two illiquid stocks are difficult to fill using pair trading engine 3 alone Because illiquid stocks often demonstrate small bid and ask sizes and wide bid-ask spreads, pair trading engine 3 will typically only issue market orders having small quantities subject to user minimums and maximums that presents the client with greater leg risk from mid-trade changes in the bid-ask prices In contrast, orde rs routed to price crossing network 5 are not confined by liquidity in the market place thereby allowing large crosses between spread traders in illiquid spreads. Accordingly, a system and method for trading pair securities is provided in which the client receives the benefits of having a pair order filled by either pair trading engine 3 pair crossing network 5 or a combination of both. A number of embodiments of the present invention have been described Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention Based on the above description, it will be obvious to one of ordinary skill to implement the system and methods of the present invention in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device Each computer program may be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired and in any case, the language may be a compiled or interpreted language Suitable processors include, by way of example, both general and special purpose microprocessors Furthermore, alternate embodiments of the invention that implement the system in hardware, firmware or a combination of both hardware and software, as well as distributing modules and or data in a different fashion will be apparent to those skilled in the art and are also within the scope of the invention In addition, it will be obvious to one of ordinary skill to use a conventional database management system such as, by way of non-limiting example, Sybase, Oracle and DB2, as a platform for implementing the present invention Also, network access devices can comprise a personal computer executing an operating system such as Microsoft Windows , U nix , or Apple Mac OS , as well as software applications, such as a JAVA program or a web browser Access devices can also be a terminal device, a palm-type computer, mobile WEB access device or other device that can adhere to a point-to-point or network communication protocol such as the Internet protocol Computers and network access devices can include a processor, RAM and or ROM memory, a display capability, an input device and hard disk or other relatively permanent storage Accordingly, other embodiments are within the scope of the following claims. It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above process, in a described product, and in the construction set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description shown in the accompanying drawing shall be i nterpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention, which, as a matter of language, might be said to fall therebetween. A method is provided for fulfilling a pair trade request and includes the steps of receiving a plurality of pair trade requests executing a transaction for a first portion of one of the plurality of pair trade requests and matching a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests. 20.The invention claimed is.1 A computer-implemented method for fulfilling a pair trade request, said pair trade request performed by a financial institution having an order inventory, the method comprising the steps of. receiving a plurality of pair trade requests, comprising at least one pair trade request, wherein said pair trade request comprises a request to trade a first security, a request to trade a second security, and a request to trade said first security and said second security with a minimum spread limit, and wherein said first security and said second security each have a bid price and an ask price. determining the bid bid spread in the market of said first security and said second security. determining the ask ask spread in the market of said first security and said second security. determining that the minimum spread limit of said pair trade request is met by a range of said bid bid spread and said ask ask spread. executing a transaction between a first portion of the trade of said first security in said one pair trade request and at least one non-pair trade request in an external market, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread and. executing a transaction between one of a second portion of said trade of said first security in said one pair trade request or a first portion of the trade of said second security in said one pair trade request, and at least one non-pair trade request in said order inventory, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread. wherein at least one of said steps is implemented with a computer.2 The method of claim 1 further comprising. executing a transaction between a portion of the trade of said second security in said one pair trade request and at least another non-pair trade request, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread. and wherein the steps of executing said first portion of the trade of said first security in said one pair trade request and executing said portion of the trade of said second security in said one pair trade request include the steps of. determining whether the bid price of the first security and the bid price of the second security meet a spread limit. determining an amount of the second security that can be sold based on a bid size associated with the second security. calculating an equivalent amount of said first security that can be bought based on the amount of said second security that can be sold. adjusting said equivalent amount of said first security based on adjustment criteria. calculating a purchase price for said adjusted equivalent amount of said first security based on the spread limit. executing an initiating order to buy said adjusted equivalent amount of said first security at said purchase price a nd. executing a covering order to sell said amount of the second security.3 The method of claim 2 wherein the step of executing a covering order to sell includes the step of. executing a covering order to sell said amount of the second security at the bid price of the second security.4 The method of claim 2 further comprising the steps of. determining whether the ask price of the first security and the ask price of the second security meet a spread limit. determining an amount of the first security that can be bought based on an offer size associated with the first security. calculating an equivalent amount of said second security that can be sold based on the amount of the second security that can be bought. adjusting said equivalent amount of said second security based on adjustment criteria. calculating a selling price for said adjusted equivalent amount of said second security based on the spread limit. executing an initiating order to sell said adjusted equivalent amount of said second se curity at said selling price and. executing a covering order to purchase said amount of the first security.5 The method of claim 4 wherein the step of executing a covering order to purchase includes the step of. executing a covering order to purchase said amount of the first security at the ask price of the first security.6 The method of claim 4 wherein said adjustment criteria include a minimum amount and a maximum amount.7 The method of claim 4 wherein the step of executing an initiating order includes the step of. rounding said initiating order to a round lot size.8 The method of claim 1 further comprising. executing a transaction between a portion of the trade of said second security in said one pair trade request and at least another non-pair trade request, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread. and wherein the steps of executing said first portion of the trade of said first security in said one pair trade request and executing said portion of the trade of said second security in said one pair trade request includes the steps of. determining whether the ask price of the first security and the ask price of the second security meet a spread limit. determining an amount of the second security that can be bought based on an ask size associated with the second security. calculating an equivalent amount of said first security that can be sold based on the amount of the second security that can be bought. adjusting said equivalent amount of said first security based on adjustment criteria. calculating a selling price for said adjusted equivalent amount of said first security based on the spread limit. executing an initiating order to sell said adjusted equivalent amount of said first security at said selling price and. executing a covering order to purchase said amount of said second security.9 The method of claim 1 wherein at least one of the executing steps include the step of. ex ecuting at least a portion of the trade of said first security or said second security in said one pair trade request in a plurality of tranches.10 The method of claim 1 wherein said plurality of pair trade requests comprises another pair trade request, wherein said another pair trade request comprises a request to trade said first security, a request to trade said second security and wherein said one pair trade request has a first spread limit and said another pair trade request has a second spread limit and wherein said method further comprises the steps of. determining that the minimum spread limit of said another pair trade request is met by said range of said bid bid spread and said ask ask spread and. matching another portion of said trade of said first security in said one pair trade request and at least another portion of said trade of said second security in said one pair trade request against said another pair trade request, provided that a range of the minimum spread limit of said one pair trade request and said another pair trade request overlaps with said range of said bid bid spread and said ask ask spread.11 The method of claim 10 wherein said matching step further includes the steps of. determining that a range of said first spread limit and said second spread limit overlaps with a market spread. setting a spread level. calculating prices for the first security and the second security that are within the market spread and based on said spread level and. matching said another portion of said trade of said first security in said one pair trade request and at least said another portion of the trade of said second security in said one pair trade request against said another pair trade request based on said calculated prices.12 The method of claim 11 wherein the step of setting a spread level includes the steps of. calculating a mean between said first spread limit and said second spread limit and. setting said spread level as said mean if said mean is within sai d market spread.13 The method of claim 12 further including the step of. identifying a spread amount that is closest to said mean and within said market spread and. setting said spread level as said spread amount if said mean is not within said market spread.14 A computer-implemented method for fulfilling a pair trade request, comprising the steps of. receiving a plurality of pair trade requests, comprising at least one pair trade request, wherein said pair trade request comprises a request to trade a first security, a request to trade a second security, and a request to trade said first security and said second security with a minimum spread limit, and wherein said first security and said second security each have a bid price and an ask price. determining the bid bid spread in the market of said first security and said second security. determining the ask ask spread in the market of said first security and said second security. determining that the minimum spread limit of said pair trade re quest is met by a range of said bid bid spread and said ask ask spread. executing a transaction between a first portion of the trade of said first security in said one pair trade request and at least a first non-pair trade request, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread. executing a transaction between a first portion of the trade of said second security in said one pair trade request and at least a second non-pair trade request, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread and. repeating the executing steps until the pair trade request is fulfilled. wherein at least one of said steps is implemented with a computer.15 The method of claim 14 wherein at least one of the repeated steps includes the step of. executing a transaction for a portion of the trade of said first security in said one pair trade re quest in an external market.16 The method of claim 14 wherein at least one of the repeated executing steps is performed by a financial institution having an order inventory and at least said one of said repeated steps includes the step of. executing a transaction for a portion of the trade of said first security in said one pair trade request against said order inventory.17 The method of claim 14 wherein said plurality of pair trade requests comprises another pair trade request, wherein said another pair trade request comprises a request to trade said first security, a request to trade said second security and a request said first security and said second security with a second minimum spread limit, the method further comprising the steps of. determining that the minimum spread limit of said another pair trade request is met by said range of said bid bid spread and said ask ask spread and. matching a second portion of said trade of said first security in said one pair trade request and at least a first portion of the trade of said second security in said one pair trade request against said another pair trade request, provided that a range of the minimum spread limit of said one pair trade request and said another pair trade request overlaps with said range of said bid bid spread and said ask ask spread.18 A computer readable storage medium storing instructions for fulfilling a pair trade request that, when executed by a computer, cause the computer to. receive a plurality of pair trade requests, comprising at least one pair trade request, wherein said pair trade request comprises a request to trade a first security, a request to trade a second security, and a request to trade said first security and said second security with a minimum spread limit, and wherein said first security and said second security each have a bid price and an ask price. determine the bid bid spread in the market of said first security and said second security. determine the ask ask spread in the ma rket of said first security and said second security. determine that the minimum spread limit of said pair trade request is met by a range of said bid bid spread and said ask ask spread. execute a transaction between a first portion of the trade of said first security in said one pair trade request and at least one non-pair trade request in an external market, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread and. execute a transaction between one of a second portion of said trade of said first security in said one pair trade request or a first portion of the trade of said second security in said one pair trade request, and at least one non-pair trade request in said order inventory, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread.19 A computer readable storage medium storing instructions for fulfilling a pair tra de request that, when executed by a computer, cause the computer to. receive a plurality of pair trade requests, comprising at least one pair trade request, wherein said pair trade request comprises a request to trade a first security, a request to trade a second security, and a request to trade said first security and said second security with a minimum spread limit, and wherein said first security and said second security each have a bid price and an ask price. determine the bid bid spread in the market of said first security and said second security. determine the ask ask spread in the market of said first security and said second security. determine that the minimum spread limit of said pair trade request is met by a range of said bid bid spread and said ask ask spread. execute a transaction between a first portion of the trade of said first security in said one pair trade request and at least a first non-pair trade request, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread. execute a transaction between a first portion of the trade of said second security in said one pair trade request and at least a second non-pair trade request, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread and. repeat the executing steps until the pair trade request is fulfilled.20 The method of claim 19 wherein at least one non-pair trade request is selected from the group consisting of an external market order and an order from an inventory from a financial institution. CROSS-REFERENCE TO RELATED APPLICATIONS. This application is a divisional application of U S patent application Ser No 10 206,549, entitled Pair trading system and method , which was filed on Jul 25, 2002 now U S Pat No 7,412,415, which claims priority to U S provisional patent application Ser No 60 334,163 entitled Method and System for Trading Pairs of S ecurities that was filed on Nov 29, 2001 The contents of both applications are herein incorporated by reference. The following invention relates to a system and method for trading securities and, in particular, for a system and method of trading securities in pairs. A recognized strategy for trading securities is known as pair-trading Pair-trading is a non-directional investment strategy in which the investor identifies two securities having similar characteristics and the securities are currently trading at a price relationship that is out of their historical trading range The investor exploits the price relationship between the securities by buying the undervalued security while short-selling the overvalued security Because pair-trading is a market-neutral strategy, it is a particularly desirable strategy for investing in volatile markets. One context in which pair trading is useful is where an investor desires to take advantage of an arbitrage opportunity resulting from a merger betwee n two companies For example, Company A has announced a definitive agreement to acquire Company T in which case Company T shareholders will receive 0 5 shares of Company A stock for each share of Company T stock they own The investor desires to capture the spread between the offered consideration 0 5 shares of A and the price of T stock To do this, the investor buys shares in T stock and sells shares of A stock. For instance, if stock T is trading at 28 per share and stock A is trading at 60 per share, then the investor may execute a trade for 200,000 spreads by buying 200,000 shares of T stock and selling 100,000 shares of A stock After the merger takes place, the investor will cover the short position in stock A with the 100,000 shares of A stock the investors receives in exchange of the 200,000 shares the investor held of stock T Thus, by executing the pair trade, the investor locks in a 400,000 profit assuming that the merger goes through The process of executing a pair trade thus in cludes executing individual trades directed to each leg of the pair trade request An example of a system for executing trades for filling a pair trade request is the Quantex system from ITG of 380 Madison Avenue, New York, N Y 10017.A challenge in implementing a pair trade is to find a counterparty for a particular position an investor desires to establish while minimizing leg risk Typically, a large pair trade is performed off the market as a private transaction negotiated by a financial institution that services large clients For example, if an investor desires to execute a pair trade betting that a proposed merger between two companies will go through, the investor would approach a financial institution seeking an investor that is willing to bet against the merger The financial institution then acts as an intermediary between the two investors in which the investors establish equal and opposite positions in the stock of the proposed merger partners thereby completing the pair trade Thus by matching two pair trade requests so that the transactions associated with each of the pair trade legs are executed simultaneously, neither investor is exposed to leg risk that would otherwise result for the period of time between execution of the first leg and the second leg of the pair trade. There are numerous drawbacks associated with the prevalent pair-trading practice First, pair-trading is typically limited to clients of large financial institutions that have the ability to identify suitable counterparties for a particular pair trade This is especially the case when the pair trade involves a large amount of stock or illiquid stocks in which the only way to execute the trade and minimize leg risk is via an off the market transaction negotiated by a financial institution Also, because a pair-trade is typically negotiated by the parties with a financial institution as an intermediary, the process is often slow and inefficient Furthermore, pair-trading under current practice i s generally best suited for large clients seeking to establish large positions thereby providing the financial institutions with the economic incentive to execute the transaction Smaller clients, however, must rely on the markets for executing pair trades, which is unsuitable for illiquid stocks and also results in increased leg risk. Accordingly, it is desirable to provide a system and method for trading securities in pairs. SUMMARY OF THE INVENTION. The present invention is directed to overcoming the drawbacks of the prior art pair trading practices Under the present invention a method is provided for fulfilling a pair trade request and includes the steps of receiving a plurality of pair trade requests executing a transaction for a first portion of one of the plurality of pair trade requests and matching a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests. In an exemplary embodiment, the method includes the step of e xecuting a transaction for a first portion of one of the plurality of pair trade requests in an external market. In another exemplary embodiment, the method includes the step of executing a transaction for a first portion of one of the plurality of pair trade requests against the order inventory. In yet another exemplary embodiment, the pair trade request includes a first security having a bid price and an ask price and a second security having a bid price and an ask price, and the method includes the steps of determining whether the bid price of the first security and the bid price of the second security meet a spread limit determining an amount of the second security that can be sold based on a bid size associated with the second security calculating an equivalent amount of the first security that can be bought based on the amount of the second security that can be sold adjusting the equivalent amount of the first security based on adjustment criteria calculating a purchase price for t he adjusted equivalent amount of the first security based on the spread limit executing an initiating order to buy the adjusted equivalent amount of the first security at the purchase price and executing a covering order to sell the amount of the second security. In still yet another exemplary embodiment, the method includes the step of executing a covering order to sell the amount of the second security at the bid price of the second security. In an exemplary embodiment, the method includes the steps of determining whether the ask price of the first security and the ask price of the second security and or the bid price of the first security and the bid price of the second security meet a spread limit determining an amount of the first security that can be bought based on an offer size associated with the first security calculating an equivalent amount of the second security that can be sold based on the amount of the second security that can be bought adjusting the equivalent amount of the second security based on adjustment criteria calculating a selling price for the adjusted equivalent amount of the second security based on the spread limit executing an initiating order to sell the adjusted equivalent amount of the second security at the selling price and executing a covering order to purchase the amount of the first security. In another exemplary embodiment, the method includes the step of executing a covering order to purchase the amount of the first security at the ask price of the first security. In yet another exemplary embodiment, the adjustment criteria include a minimum amount and a maximum amount. In still yet another exemplary embodiment, the method includes the step of rounding the initiating order to a round lot size. In an exemplary embodiment, the method includes the step of executing a first portion of one of the plurality of pair trade requests in a plurality of tranches. In another exemplary embodiment, the one of the plurality of pair trade requests a nd the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit and the another of said plurality of trade requests has a second spread limit and wherein the method includes the steps of determining that a range of the first spread limit and the second spread limit overlaps with a market spread setting a spread level calculating prices for the first security and the second security that are within the market spread and based on the spread level and matching the second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests based on the calculated prices. In yet another exemplary embodiment, the method includes the steps of calculating a mean between the first spread limit and the second spread limit and setting the spread level as the mean if the mean is within the market spread. In still yet another exemplary embodimen t, the method includes the step of identifying a spread amount that is closest to the mean and within the market spread and setting the spread level as the spread amount if the mean is not within the market spread. In an exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit, a buy ratio and a sell ratio, the another of the plurality of trade requests has a second spread limit, a buy ratio and a sell ratio and the method includes the steps of determining that the buy ratio and the sell ratio associated with the one of the plurality of trade requests does not equal the buy ratio and the sell ratio of the another of the plurality of trade requests and that an overlap exists between range of the first spread limit and the second spread limit and a market spread determining that market prices exist tha t are within the overlap determining a mismatch amount in the second security based on a difference between the buy ratio and the sell ratio associated with the one of the plurality of trade requests and the buy ratio and the sell ratio of the another of the plurality of trade requests calculating a cross amount for the first security and the second security selecting a crossing price for the first security and the second security that is within the overlap determining that the mismatch amount is available at the crossing price for the second security matching the second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests based on the calculated prices and executing a transaction for the mismatch amount of the second security at the crossing price for the second security. In another exemplary embodiment, the method includes the step of determining that the mismatch amount is available in an external market at the crossing pr ice for the second security. In yet another exemplary embodiment, the method is performed by a financial institution having order inventory and includes the step of determining that the mismatch amount is available in the order inventory at the crossing price for the second security. In still yet another exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests indicate a number of spreads and the method includes the step of matching a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests if the number of spreads is greater than a minimum number of spreads. In an exemplary embodiment, the method includes the step of receiving a preference for filling at least some of the plurality of trade requests via the step of executing a transaction for a first portion of one of the plurality of pair trade requests, described above. In another exemplary embodiment, th e method includes the step of receiving a preference for filling at least some of the plurality of trade requests via the step of matching a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests, described above. Under the present invention, a method for fulfilling a pair trade request is provided and includes the steps of receiving a plurality of pair trade requests and matching at least a portion of one of the plurality of pair trade requests against another of the plurality of pair trade requests. Under the present invention, a system for fulfilling a pair trade request is provided, the system receiving a plurality of pair trade requests and includes a pair trading engine for executing a transaction for a first portion of one of the plurality of pair trade requests The system also includes a pair crossing network for matching a second portion of said one of the plurality of pair trade requests against another of the p lurality of pair trade requests. In an exemplary embodiment, the system includes a link to external markets and wherein the pair trading engine executes the transaction for the first portion of one of the plurality of pair trade requests in the external markets. In another exemplary embodiment, the system includes a financial institution having an order inventory and wherein the pair trading engine executes the transaction for the first portion of one of the plurality of pair trade requests against the order inventory. In yet another exemplary embodiment, the pair trade request includes a first security having a bid price and an ask price and a second security having a bid price and an ask price, and wherein the pair trading engine determines whether the bid price of the first security and the bid price of the second security meet a spread limit determines an amount of the second security that can be sold based on a bid size associated with the second security calculates an equivalent amo unt of the first security that can be bought based on the amount of the second security that can be sold adjusts the equivalent amount of the first security based on adjustment criteria calculates a purchase price for the adjusted equivalent amount of the first security based on the spread limit executes an initiating order to buy said adjusted equivalent amount of the first security at the purchase price and executes a covering order to sell the amount of the second security. In still yet another exemplary embodiment, the pair trading engine executes a covering order to sell the amount of the second security at the bid price of the second security. In an exemplary embodiment, the pair trading engine determines whether the ask price of the first security and the ask price of the second security meet a spread limit determines an amount of the first security that can be bought based on an offer size associated with the first security calculates an equivalent amount of the second security t hat can be sold based on the amount of the second security that can be bought adjusts said equivalent amount of the second security based on adjustment criteria calculates a selling price for the adjusted equivalent amount of the second security based on the spread limit executes an initiating order to sell the adjusted equivalent amount of the second security at the selling price and executes a covering order to purchase the amount of the first security. In another exemplary embodiment, the pair trading engine executes a covering order to purchase the amount of the first security at the ask price of the first security. In yet another exemplary embodiment, the pair trading engine rounds the initiating order to a round lot size. In still yet another exemplary embodiment, the pair trading engine executes a first portion of one of the plurality of pair trade requests in a plurality of tranches. In an exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit and the another of the plurality of trade requests has a second spread limit and wherein the pair crossing network determines that a range of the first spread limit and the second spread limit overlaps with a market spread sets a spread level calculates prices for the first security and the second security that are within the market spread and based on the spread level and matches the second portion of said one of the plurality of pair trade requests against another of the plurality of pair trade requests based on the calculated prices. In another exemplary embodiment, the pair crossing network calculates a mean between the first spread limit and the second spread limit and sets the spread level as the mean if the mean is within the market spread. In yet another exemplary embodiment, the pair crossing network identifies a spread amount that is closest to the mean and within the market spread and sets the spread level as the spread amount if the mean is not within the market spread. In still yet another exemplary embodiment, the one of said plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit, a buy ratio and a sell ratio, the another of the plurality of trade requests has a second spread limit, a buy ratio and a sell ratio and wherein the pair crossing network determines that the buy ratio and the sell ratio associated with the one of the plurality of trade requests does not equal the buy ratio and the sell ratio of the another of the plurality of trade requests and that an overlap exists between range of the first spread limit and the second spread limit and a market spread determines that market prices exist that are within the overlap determines a mismatch amou nt in the second security based on a difference between the buy ratio and the sell ratio associated with the one of the plurality of trade requests and the buy ratio and the sell ratio of the another of the plurality of trade requests calculates a cross amount for the first security and the second security selects a crossing price for the first security and the second security that is within said overlap determines that the mismatch amount is available at the crossing price for the second security matches the second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests based on the calculated prices and executes a transaction for the mismatch amount of the second security at the crossing price for the second security. In an exemplary embodiment, the pair crossing network determines that the mismatch amount is available in an external market at the crossing price for the second security. In another exemplary embodiment, the pair crossing network determines that the mismatch amount is available in the order inventory at the crossing price for the second security. In yet another exemplary embodiment, the one of said plurality of pair trade requests and the another of the plurality of pair trade requests indicate a number of spreads and wherein the pair crossing network matches a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests if the number of spreads is greater than a minimum number of spreads. In still yet another exemplary embodiment, the plurality of pair trade requests include at least some pair trade requests indicating a preference for execution via said pair crossing network, and the system further includes a portfolio manager in communications with the pair crossing network, the portfolio manager receiving the plurality of pair trade requests and routing the at least some pair trade requests to the pair crossing network according to the preference. In an exemplary embodiment, the system includes a pair trading engine for executing at least some of the plurality of pair trade requests, further includes a portfolio manager in communications with the pair trading engine and wherein the plurality of pair trade requests include at least some pair trade requests indicating a preference for execution via the pair trading engine, the portfolio manager receiving the plurality of pair trade requests and routing the at least some of the plurality of trade requests to the pair trading engine according to the preference. Under the present invention, a system for fulfilling a pair trade request is provided, wherein the system receives a plurality of pair trade requests and includes a pair crossing network for matching at least one of the plurality of pair trade requests against another of the plurality of pair trade requests. Accordingly, a method and a system are provided for trading pair securities. The invention accordingly com prises the features of construction, combination of elements and arrangement of parts that will be exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims Other features and advantages of the invention will be apparent from the description, the drawings and the claims. DESCRIPTION OF THE DRAWINGS. For a fuller understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawings, in which. FIG 1 is a block diagram of a system for trading securities in pairs according to the present invention. FIG 2 is a flowchart of the steps a pair trading engine included in the system of FIG 1 applies to fill a pair trade request. FIG 3 is a flowchart of the steps a pair crossing network included in the system of FIG 1 applies to fill a pair trade request. FIG 4 is a flowchart of a process by which the pair crossing network of the system of FIG 1 fills imperfectly matched orders and. FIG 5 i s a graph for identifying the market prices for two securities that meet the required spread limits. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS. Referring now to FIG 1 there is shown a block diagram of a system 1 for trading securities in pairs according to the present invention System 1 receives pair trade requests from clients operating client access devices 7 and attempts to fill the pair trade requests according to the parameters associated with the particular pair trade request System 1 includes two different subsystems for filling pair trade requests a pair trading engine 3 and a pair crossing network 5 As will be described below, pair trading engine 3 receives a pair trade request and attempts to fill in whole or in part the trade request by executing the appropriate trades in an external market 13 that may include, by way of non-limiting example, the New York Stock Exchange, the NASDAQ or any other financial market Pair trading engine 3 may also fill in whole or in part a pair trade request by executing a transaction against order inventory 11 of non-pair trade requests controlled by the financial institution that is operating system 1 In addition, pair trading engine may also fill in whole or in part a pair trade request by forwarding the trade request to pair crossing network 5 for matching with other pair trade requests. Likewise, pair crossing network 5 receives a pair trade request and fulfills in whole or in part the request by matching it against another pair trade request received by pair crossing network 5 by matching the request against inventory 11 controlled by the financial institution and or by forwarding the trade request to pair trading engine 3 for execution in external markets 13.System 1 also includes a portfolio manager 9 that may be, for example, a software program executing on a computer system that receives the pair trade requests from client access device 7 and presents the trade request to either pair trading engine 3 pair crossi ng network 5 or both, depending on the trade parameters set by the client Also, the client may query portfolio manager 9 regarding the status of any pair trade request the client has presented to system 1.In operation, system 1 may fulfill a pair trade request either using pair trading engine 3 or pair crossing network 5 or a combination of the two For example, a pair trade request received by system 1 may be completely filled by pair trading engine 3 as follows. Assume a case where XYZ is taking over ABC and is offering 0 575 shares of XYZ for each ABC share and investor Arb wants to invest in the price difference between ABC stock and XYZ stock To take advantage of the price difference, Arb wants to lock in the difference between the value offered 0 575 XYZ stock and the value of ABC stock by buying ABC stock and selling XYZ stock subject to the condition that ABC 0 575 XYZ 1 19 i e Arb desires to capture a 1 19 difference between XYZ s takeover offer and ABC s share price. In order to fill this pair trade, Arb presents a pair trade request to portfolio manager 9 using client access device 7 The pair trade request typically includes a number of parameters that define the pair trade and that also may be used by portfolio manager 9 in determining how the pair trade request is to be filled Arb typically indicates in the trade request the number of spreads the Arb desires to invest in and also provides a minimum and maximum share amount that he is willing to trade per tranche. For example, Arb may indicate a desire to invest in 100,000 spreads and may only wish to trade the spread 3,000-8,000 shares at a time Arb generally sets this tranche size range based on the liquidity and volatility of ABC stock and XYZ stock Arb may set a larger minimum tranche size if ABC stock and XYZ stock are fairly liquid stocks because higher liquidity increases the likelihood that a larger tranche size will be executed Arb may set a lower maximum tranche size if XYZ stock and ABC stock are volatile stocks so as to limit the leg risk associated with executing a pair trade. Yet another pair trade parameter Arb provides is the spread limit in the above case 1 19 which is the amount Arb desires to capture in the trade Arb does not have to provide, however, the discrete prices at which trades for ABC and XYZ stock are to be executed as these prices are calculated by pair trading engine 3 and or pair crossing network 5 , as will be described below. Referring now to FIG 2 there is shown a flowchart describing the steps pair trading engine 3 applies to fill a pair trade request The flowchart in FIG 2 is based on the above example and the market data listed in Table 1 below. Initially, in Step 201 pair trading engine 3 determines whether the bid bid prices or ask ask prices of ABC and XYZ stock, respectively, meet the spread limit requirement of the particular pair trade request In this case the bid bid spread is 1 4375 122 50 0 575 69 and the ask ask spread is 1 1969 122 625 0 575 69 3125 so that each spread is less than the spread limit of 1 19, as is required for this particular trade Once it is determined that either the bid bid spread or the ask ask spread meets the spread limit, then in Step 202 it is determined as is indicated in Table 1 how much XYZ stock can be sold at the bid and how much ABC stock can be bought at the ask In an exemplary embodiment, the client may specify whether the bid bid spread, the ask ask spread or either the bid bid or the ask ask spread must exceed the indicated spread limit for a transaction to proceed If neither the bid bid spread nor the ask ask spread meets the spread limit, the process waits a period of time for example 0 10 seconds and returns to Step 201 to again test whether the bid bid spread or the ask ask spread meets the spread limit. Next, in step 203 an equivalent amount of stock that can be sent into the market i e bought sold in the market is calculated for a spread based on the bid bid price spread and or the as k ask price spread that meets the spread limit In this example, if a maximum of 10,000 shares of XYZ stock can be sold into the market i e the XYZ bid size then, based on the ABC XYZ ratio of 1 0 575 in this case , a total of 17,391 10,000 0 575 shares of ABC stock are to be bought in order to execute a balanced pair trade Likewise, if a maximum of 1,500 shares of ABC stock can be bought in the market i e the ABC ask size , then, based on the ABC XYZ ratio of 1 0 575 in this case , a total of 863 1500 0 575 shares of XYZ stock are to be sold in order to execute a balanced pair trade. Next, in Step 204 the pair trade share amounts calculated in Step 203 are adjusted to conform to the wave maximum and minimum parameters i e the maximum minimum tranche size included in the pair trade request as well as market round lot limits In the above example, the amount of ABC shares to be bought that was calculated based on the XYZ bid size i e 17,391 is first rounded to an even lot size i e 17,400 a nd then reduced to the maximum tranche size of 8000 Also, the amount of XYZ shares to be offered that was calculated based on the ABC ask size i e 863 is first rounded to an even lot size i e 900 and then increased to 1,700 shares to meet the minimum tranche size of 3000 3000 0 575 1777 In an exemplary embodiment the minimum and maximum tranche size is scaled by the particular ratio for example, in the above case, the tranche sizes for XYZ stock is scaled by 0 575 In another embodiment, the maximum minimum tranche size is used for each security in the pair trade request without scaling In yet another exemplary embodiment, the pair trade request includes a separate maximum minimum tranche for each security. Once the share amounts for the pair trade are calculated, in Step 205 the share prices that are needed to meet the spread limit of the pair trade request are calculated For example, for a pair trade based on the bid bid price spread, in order to meet the spread limit of 1 19 credit, t he price at which ABC stock is to be bid should be no greater than 69 2475 122 50 0 575 1 19 a share Likewise, for a pair trade based on the ask ask price spread, in order to meet the spread limit, the price at which XYZ stock is to be offered should be greater than or equal to 122 6130 69 3125 1 19 0 575 a share. Next, once the pair trade share amounts and share prices have been calculated, in Step 206 pair trading engine 3 sends initiating orders to external markets 13 in order to fill the pair trade request The initiating orders may include an initiating order for executing a pair trade based on the bid bid spread in this case a bid for 8,000 shares of ABC stock at 69 2475 and or an initiating order for executing a pair trade based on the ask ask spread in this case an offer of 1,700 shares of XYZ stock at 122 6130.Finally, as the initiating orders sent to external markets 13 in Step 207 get filled, pair trading engine 3 automatically sends into the market the covering side of the pa ir trade So, for example, as the initiating order of buying 8,000 shares of ABC stock at 69 2475 gets filled, pair trading engine 3 sends an order to external markets 13 to sell 4,600 8,000 0 575 shares of XYZ stock at 122 50.In an exemplary embodiment, the client s pair trade request includes threshold amounts that indicate the amount of variance in stock price and or share amount the client is willing to absorb For example, if in the process of covering the initiating order the price of XYZ stock dips to 122 49 in which case the spread limit of the pair trade would drop to 1 18 , then pair trading engine 3 would still sell XYZ stock at the price of 122 49 if the 0 01 difference was within the threshold amount included in the pair trade request Similarly, the pair trade request may include threshold amounts for any other pair trade parameter, including by way of non-limiting example, the number of spreads to be purchased and the tranche sizes If, however, a particular threshold amount indicated by the client is exceeded for any given pair trade parameter, then pair trading engine 3 would attempt to cancel the initiating order and or the covering order that may be possible if the orders have not yet reached the market or have not yet been filled In such a case, pair trading engine 3 would then repeat the above analysis for determining suitable initiating and cover orders. To fill a pair trade request, pair trading engine 3 executes trades utilizing the method described above Typically, pair trading engine 3 tranches a pair trade request and trades piece-meal in external markets 13 In certain cases, however, it may be difficult to fill a trade request by executing several transactions in external markets 13 either because the pair trade request is for a very large number of spreads or includes stocks that are illiquid in which cases pair trading engine 3 may be ineffective in filling the pair trade request Also, in certain situations, a client wishing to remain anonym ous may indicate in the pair trade request a preference that no orders be sent to external markets 13 In these circumstances, portfolio manager 9 may route the particular pair trade request to pair crossing network 5.Referring now to FIG 3 there is shown a flowchart illustrating the steps pair crossing network 5 applies to fill a pair trade request The flowchart in FIG 3 is based on the above example and the market data listed in Table 2 below. Spread Limit as defined by 0 575 XYZ ABC. Continuing the previous example, assume the pair trade request issued by Arb for 100,000 spreads was half-filled by pair trading engine 3 Also, assume that system 1 receives a pair trade request from Antiarb that indicates a desire to sell 30,000 shares of ABC and buy 17,200 shares a ratio of 1 0 575 and also indicates a spread limit of 1 30 i e ABC 0 575XYZ 1 30 In this case Arb and Antiarb s orders are complimentary in the primary order elements securities, ratios and buy versus sell Also, Antiarb is willing to pay 0 11 per spread more than Arb is demanding from the marketplace Based on these parameters, there is an opportunity for Arb s and Antiarb s trade requests to be filled via pair crossing network 5.If Antiarb s pair trade request was marked for trading by pair trading engine 3 then portfolio manager 9 sends Antiarb s order to pair trading engine 3 for execution Pair trading engine 3 then sends the parameters of Antiarb s trade request, as well as all orders waiting for execution in pair trading engine 3 to pair crossing network 5 Pair crossing network 5 will recognize as described above that there is a crossing opportunity between Arb s order and Antiarb s order In this case, pair crossing network 5 then directs pair trading engine 3 to suspend the execution of Antiarb s order in the amount that can be crossed by pair crossing network 5 30,000 spreads in this case In addition, pair trading engine 3 routes a cross amount of 30,000 spreads from Arb s order to pair crossing network 5 for crossing against Antiarb s order At this point, the pair crossing network 5 crosses the Antiarb order against a portion of Arb s order, as follows. Assume the prevailing market conditions at the time of the cross are as shown in Table 3 Furthermore, Table 3 indicates the XYZ Ratio-Adjusted Value for both the bid and ask prices based on the conversion ratio of 1 0 575 Based on the XYZ Ratio-Adjusted Values, a Bid Ask Spread Range i e the spread provided for a cross between the bid price of ABC stock and the XYZ Ratio-Adjusted ask price of 1 3863 is calculated and an Ask Bid Spread Range i e the spread provided for a cross between the ask price of ABC stock and the XYZ Ratio-Adjusted bid price of 1 05 is calculated. To perform the cross, in Step 301 pair crossing network 5 first determines whether the range of spread limits associated with Arb s and Antiarb s trade requests i e 1 30- 1 19 coincides with the range of the prevailing market spread 1 3863- 1 05 In this example, the range of spread limits does coincide with the prevailing market spread because at least a portion of the spread limit range overlaps with a portion of the market spread Thus, a cross can occur. Next, in Step 302 pair crossing network 5 calculates the mean of Arb s and Antiarb s spread order limit which is 1 30 1 19 2 1 245 and determines whether the mean is within the range of the market spread i e 1 3863- 1 05 If it is, then in Step 303 pair cros sing network 5 calculates the prices at which to cross The prices must be within the current markets for ABC stock and XYZ stock, and satisfy market uptick requirements for short sales , and provide a spread that is equal to the spread level calculated above For example, with the inside market for ABC stock at 70 00-70 25 and the inside market for XYZ stock at 124 00-124 15, a cross price of 70 11 for ABC stock and 124 096 for XYZ stock provides the spread of 1 2452 thereby meeting the requirement of both Arb s and Antiarb s trade request Finally, in Step 304 pair crossing network 5 crosses 30,000 shares of ABC stock at 70 11 with Arb buying and Antiarb selling and 17,200 shares of XYZ at 124 096 with Arb selling and Antiarb buying. If it is determined in Step 302 that the mean of Arb s and Antiarb s spread order limits does not fall within the range of the market spread, then in Step 305 the spread closest to the mean of the two spread limits that is also within the market spread is ca lculated For example, if the market spread is 1 3863- 1 28, then the mean of the two spread limits 1 245 is not within the market spread In such a case, 1 28 is selected as the spread level that is closest to the mean and within the market spread In an exemplary embodiment, the spread level at which Arb and Antiarb cross can be determined in any other suitable manner as long as the spread level is within the market spread and within the range of spread limits indicated in the pair trade requests. Once the spread level is determined, the method proceeds to Step 303 in which pair crossing network 5 calculates prices to cross at that are within the current markets for ABC stock and XYZ stock and that meet the calculated spread level In the case where the calculated spread level is 1 28, the cross will occur at a price of 70 08 for ABC stock and 124 1043 for XYZ stock Finally, the method proceeds to Step 304 in which pair crossing network 5 performs the cross between Arb and Antiarb. Once a pair trade request is filled or partially filled , the transaction details are reported to portfolio manager 9 and made available to the client operating client access device 7.In the previous example, pair crossing network 5 crosses orders in which both Arb and Antiarb desire to trade the same pair of securities in the same ratio In an exemplary embodiment, pair crossing network 5 executes a cross between two pair trade requests that are not perfectly matched. For example, assume that pair crossing network 5 receives the pair trade requests as shown in Table 4 Note that these two pair trade requests are imperfectly matched because each trade request uses a different ratio between ABC and XYZ stock. Arb s Spread Limit is defined by 0 575 XYZ ABC Antiarb s Spread Limit is defined by 0 6 XYZ ABC. Also, assume the market in ABC and XYZ stocks at the time the pair trade requests are received by pair crossing network 5 is as described in Table 5 below. Arb s XYZ Ratio-Adjusted Value. Arb s Dollar Range. AntiArb s XYZ Ratio-Adjusted Value. AntiArb s Dollar Range. Referring now to FIG 4 there is shown a flowchart illustrating a process by which pair crossing network 5 fills these imperfectly matched order First, in Step 401 pair crossing network 5 determines whether Arb s buy security equals Antiarb s sell security and whether Arb s sell security equals Antiarb s buy security If both conditions are not met, then a cross between the two orders cannot occur If the two conditions are met, then in Step 402 it is determined whether Arb s buy ratio equals Antiarb s sell ratio and whether Arb s sell ratio equals Antiarb s buy ratio If these ratios are the same, then pair crossing network 5 proceeds t o cross the two orders as described in the example above Note that for a cross to occur at this stage does not require the ratios themselves to match but rather that the ratios of the ratios match for e g a ratio of 2 3 matches a ratio of 0 667 1.If, however, the two ratios are not equal as in this case where Arb s sell ratio does not equal Antiarb s buy ratio , then in Step 403 pair crossing network determines whether there is an overlap between Arb s and Antiarb s spread limit that also falls within the bid ask market for ABC and XYZ stock To make such a determination, pair crossing network 5 calculates whether there are market prices for both ABC and XYZ stock that satisfy the following inequalities L 1 Ratio A ABC Ratio B XYZ and 1 L 2 Ratio C ABC Ratio D XYZ 2 Where L 1 is Arb s spread limit of 1 19 credit, L 2 is Antiarb s spread limit of 4 40 debit, RatioA is Arb s buy ratio of 1 1, RatioB is Arb s sell ratio of 1 0 575, RatioC is Antiarb s sell ratio of 1 1 and RatioD is Antiar b s buy ratio of 1 0 6.Referring now to FIG 5 there is shown a graph 51 that depicts market prices for ABC and XYZ stock that meet the spread limits of Arb and Antiarb In graph 51 the x-axis represents the prices for XYZ stock while the y-axis represents the prices for ABC stock Graph 51 includes a shaded area 53 that is the universe of market prices for ABC and XYZ stock that could satisfy the spread trade involving those stocks Also included in graph 53 is a spread limit line L 1 inequality 1 , above that represents the spread limit associated with Arb and a spread limit line L 2 inequality 2 , above that represents the spread limit associated with Antiarb Thus, the solution set of market prices that satisfies inequalities 1 and 2 is the portion of dark shared area 53 that falls between spread limit line L 1 and spread limit line L 2 In this example, a cross at a share price for ABC of 70 14 and a share price of 124 15 for XYZ stock meets the investor s spread limits and falls within the market prices for ABC and XYZ stock. If it is determined that no share prices for both ABC and XYZ stock satisfy Arb s and Antiarb s spread limits, then no cross can occur If such share prices do exist, then in Step 404 it is determined which of the investors desires to transact in fewer shares of ABC stock and a mismatch in share amounts caused by the differing ratios is determined In our example, Antiarb desires to sell fewer ABC shares than Arb desires to buy 30,000 vs 50,000 Then, in Step 405 pair crossing network 5 determines the number of XYZ shares that can be crossed between Arb and Antiarb based on the maximum amount of ABC shares that can be crossed 30,000 in this example Based on the Antiarb ABC order quantity of 30,000 shares, the maximum number of XYZ shares that Arb will cross with Antiarb is.30 000 Arb XYZ Ratio Arb ABC Ratio 30 000 0 575 1 17 300 17 250 rounded to an even lotsize. While the maximum quantity of XYZ shares that Arb will cross is 17,300, Antiarb s trade request indicates a desire to cross 18,000 shares To overcome this imbalance, in Step 406 pair crossing network 5 is in communications with external markets 13 for determining whether the excess 700 XYZ shares needed to satisfy Antiarb s trade request can be transacted for in external markets 13 In an exemplary embodiment, pair crossing network 5 makes this determination by issuing a query to pair trading engine 3 as to whether 700 shares of XYZ stock can be bought in external markets 13 Because, as indicated in Table 5, 3,000 shares of XYZ stock are offered at 124 15, pair trading engine 3 responds to pair crossing network 5 that the 700 shares needed to balance the cross between Arb and Antiarb are available from external markets 13 at 124 15.Next, in Step 407 pair crossing network calculates the cross prices that are necessary such that Arb and Antiarb achieve their respective spread limits while also incorporating the excess 700 shares of XYZ stock that must be purchased from exte rnal markets 13 at 124 15 to satisfy Antiarb s trade request An example of such cross prices that meet these criteria is a price of 70 14 for ABC stock and a price of 124 15 for XYZ stock. Once the cross prices are calculated, in Step 408 pair crossing network 5 crosses 30,000 shares of ABC stock and 17,300 shares of XYZ stock between Arb and Antiarb and also buys 700 shares of XYZ stock at 124 15 in external markets 13 on behalf of Antiarb Thus, both Arb and Antiarb s pair trade requests are satisfied. Alternatively, the entire 18,000 shares of XYZ stock may be crossed thereby fully satisfying Antiarb s trade request In such a case, the ratio mismatch is addressed by Arb purchasing an additional 1200 700 0 575 rounded to a lotsize shares of ABC stock from external market 13 or from firm inventory 11.Once the trade is completed, the details of the transaction are provided to portfolio manager 9 to report the transaction details to the investors. In an exemplary embodiment, a pair order or portion thereof may be filled against an internal inventory 11 of trade requests maintained by the financial institution operating system 1 For example, in the previous example in which an excess of 700 shares of XYZ stock needs to be purchased in order for a match i e cross between Arb and Antiarb s trade requests to occur, instead of determining whether the 700 shares are available in external markets 3 pair crossing network 5 examines firm inventory 11 to determine whether the shares are available at the required price Likewise, in cases where pair trading engine 3 desires to execute a pair trade based on orders to be sent to external markets 13 pair trading engine 3 may first determine whether the order can be filled, in whole or in part, using trade requests pending in firm inventory 11 Generally, the advantages of filling an order using pending trade requests in firm inventory 11 is that execution is faster, transaction costs are lower and leg risk is minimized. In another exempl ary embodiment, a client s pair trade request may also include a minimum number of spreads that can be traded in pair crossing network 5 Also, pair crossing network 5 may be designed to require a minimum share amount for a cross to occur A minimum number of spreads that can be traded may be provided in order to reduce the distractions and booking costs associated with numerous smaller trades that may exceed the benefits of a de minimis fill. In another exemplary embodiment, portfolio manager 9 publishes the inside cross market for any pair that a client has selected for crossing in pair crossing network 5 In still another exemplary embodiment, the client has the option for each pair trade selected for crossing in pair crossing network 5 to designate that the order should be reflected in the published inside cross market This inside cross market consists of the tightest spread bid and offer and corresponding bid size and offer size from all client pair orders pending in pair crossing net work 5 In this way, a client can assess the likelihood and timing of a pair trade request being filled by pair crossing network 5 Also, by publishing the client s spread interest, others seeking liquidity can trade at the client s level. In an exemplary embodiment, the client can designate each pair order designated for pair trading engine 3 and or pair crossing network 5 for Broker Negotiation If Broker Negotiation is designated, the client s broker-dealer sales representative is notified of the client s spread order thereby prompting the broker-dealer to solicit a complementary, agency order from another client The client may also designate each pair order for Broker Facilitation in which case the client allows the broker-dealer to act principally to fill the client s order. In summary, the advantages to a client of using pair trading engine 3 is that pair trading engine 3 allows the client to trade a spread order while limiting leg risk or the risk of missing a targeted spread level T his is accomplished by breaking the total order into tranches of sizes proportionate to the market, subject to user minimums and maximums, that can be traded in external markets 13 or against firm inventory 11 Orders executed via pair trading engine 3 however, are typically of a lower traded volume because trading is constrained to the liquidity available in the market In contrast, trades executed via pair crossing network 5 are not constrained by market liquidity and do not have to be tranched to minimize leg risk In particular, the benefits of filling a pair trade request via pair crossing network 5 are as follows. Elimination of Leg Risk Pair crossing network 5 potentially provides a deeper well of liquidity because the trades are brokered, as a spread, directly between spread investors via a central clearing facility Moreover, the introduction and use of a pair trading facility eliminates the leg risk described above without a sacrifice of liquidity. Large Transactions Only Certain l arge investors may prefer to use pair crossing network 5 rather than pair trading engine 3 to avoid having a trade request broken up into numerous small executions For example, sudden, brief moves in one of the two stocks included in the pair trade request may cause pair trading engine 3 to issue numerous small executions to fill the request While a small investor may welcome capturing these small opportunities, a large investor may find such small executions to be more of a nuisance than a service. Price Setting versus Price Taking Large investors seeking liquidity may prefer to set their price via the pair crossing network 5 Also, other spread investors looking for liquidity can use pair crossing network 5 to monitor and trade with the large investor at the large investor s level While client orders directed to pair trading engine 3 can designate a spread limit, such orders are essentially price-takers as the market reaches the desired level, the orders are executed Moreover, the pair trading engine tranching mechanism creates relatively small orders, allowing institutional flows to move the individual stocks As a result, the small, tranched orders generated by pair trading engine 3 can become overpowered by single-name institutional flows In addition, orders designated solely for pair trading engine 3 and not for pair crossing network 5 are not published to a central quote facility such as by portfolio manager 9 thereby preventing other spread traders from knowing the size and limit of a pair trading engine order. Illiquid Stocks vs Liquid Stocks Spreads that include one or two illiquid stocks are difficult to fill using pair trading engine 3 alone Because illiquid stocks often demonstrate small bid and ask sizes and wide bid-ask spreads, pair trading engine 3 will typically only issue market orders having small quantities subject to user minimums and maximums that presents the client with greater leg risk from mid-trade changes in the bid-ask prices In contrast, o rders routed to price crossing network 5 are not confined by liquidity in the market place thereby allowing large crosses between spread traders in illiquid spreads. Accordingly, a system and method for trading pair securities is provided in which the client receives the benefits of having a pair order filled by either pair trading engine 3 pair crossing network 5 or a combination of both. A number of embodiments of the present invention have been described Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention Based on the above description, it will be obvious to one of ordinary skill to implement the system and methods of the present invention in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device Each computer program may be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired and in any case, the language may be a compiled or interpreted language Suitable processors include, by way of example, both general and special purpose microprocessors Furthermore, alternate embodiments of the invention that implement the system in hardware, firmware or a combination of both hardware and software, as well as distributing modules and or data in a different fashion will be apparent to those skilled in the art and are also within the scope of the invention In addition, it will be obvious to one of ordinary skill to use a conventional database management system such as, by way of non-limiting example, Sybase, Oracle and DB2, as a platform for implementing the present invention Also, network access devices can comprise a personal computer executing an operating system such as Microsoft Windows , Unix , or Apple Mac OS , as well as software applications, such as a JAVA program or a web browser Access devices can also be a terminal device, a palm-type computer, mobile WEB access device or other device that can adhere to a point-to-point or network communication protocol such as the Internet protocol Computers and network access devices can include a processor, RAM and or ROM memory, a display capability, an input device and hard disk or other relatively permanent storage Accordingly, other embodiments are within the scope of the following claims. It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above process, in a described product, and in the construction set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description shown in the accompanying drawing shall b e interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention, which, as a matter of language, might be said to fall therebetween.