Abstract:
A posting market center and process are disclosed for maintaining a market center-restricted order on a selected market center. The market center and process disclosed aggressively maintain a market center-restricted order that would normally lock or cross an away market by initially pricing the order a tick increment away from the contra side market best bid or offer and then dynamically re-pricing the order in increasing aggressiveness as the away market best bid or offer moves its quotes further away from the order&#39;s currently displayed price. The disclosed market center-restricted order stands its ground to an updated away market best bid or offer that moves to its price or through it.

Description:
BACKGROUND 
     Regulations and established rules dictate how financial instrument market centers, including securities market centers, must interact with one another and, specifically, how orders are to be handled among market centers. Some present market center rules and regulations for some markets dictate that when an order is placed on a market center, it is to be executed at the best bid or offer price presently available in the entire market (“Market Best Bid” or “Market Best Offer”), regardless of whether the market center that the order was sent to is presently offering the best bid or best offer price. If a market center receives an incoming marketable order (i.e. an order whose price is at or better than the opposite side Market Best Bid or Best Offer price) and cannot match that order within its own order book, then that market center must route all or part of the order to the market center then presently posting the Market Best Bid or Best Offer price. 
     While these rules and regulations are designed to give a securities trader the benefit of having his order executed at the best price available in the market at the time, traders sometimes want their orders only executed on the market center to which they sent the order, trading off speed of execution versus best price. These traders do not want their orders to leave the market center to which it was sent. Traders can make this request as long as their order does not lock or cross the away market. A trader&#39;s order would lock the away market if the trader&#39;s order price has the same price as the Market Best Bid or Best Offer price then available on the opposing side of the market (i.e. the trader&#39;s buy order price is equal to the Market Best Offer price or the trader&#39;s sell price is equal to the Market Best Bid price). A trader&#39;s order price would cross the away market if a trader&#39;s buy order price is higher than the Market Best Offer price or if a trader&#39;s sell order price is lower than the Market Best Bid price. 
     In prior systems, if a trader&#39;s market center-restricted order locked or crossed the away market, it was typically canceled. Traders in such systems typically had to choose between pricing an order aggressively to maximize trading opportunities or risk having the order cancelled because the trader had priced it through the market (i.e. priced it so that it would lock or cross the away market). 
     Accordingly, there is a need for a market center order processing method and system where a trader can designate that an order only execute on a specific market center and that order will only re-price more aggressively than its current posted price and not fade from its current posted price as prices on an away market move to or through it. 
     SUMMARY 
     According to an aspect of the present invention, a method for processing an incoming market center-restricted order includes providing a posting market center having a public order book and providing a tick back increment. It further includes receiving a market center-restricted order specifying a financial instrument and a price and retrieving an away market best price in the specified financial instrument. It further includes determining whether the price of the market center-restricted order locks or crosses the best away market price, such that when the price of the market restricted order locks or crosses the best away market price, a ticked back price parameter is computed based on the away market best price and the tick back increment and where the computed ticked back price parameter is displayed as the market center-restricted order price on the posting market center public order book. The method further includes retrieving an updated away market best price, where the updated away market best price has moved to or through the price displayed for the market center-restricted order such that the updated away market best price locks or crosses the posting market center public order book and maintaining the price displayed for the market center-restricted order in the posting market center public order book. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings where: 
         FIG. 1  is a block diagram illustrating the trading environment in which an embodiment of the present invention operates; 
         FIG. 2  is a flow diagram illustrating a process implemented by an embodiment of the present invention for incoming market center-restricted buy orders; 
         FIG. 3  is a flow diagram illustrating a process implemented by an embodiment of the present invention where ticked back buy orders are re-evaluated in view of an updated market best offer price; 
         FIG. 4  is a flow diagram illustrating a process implemented by an embodiment of the present invention for incoming market center-restricted sell orders; and 
         FIG. 5  is a flow diagram illustrating a process implemented by an embodiment of the present invention where ticked back buy orders are re-evaluated in view of an updated market best bid price. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a trading environment in which an embodiment of the system and method of the present invention operates is depicted. The examples discussed herein describe the use and application of the present invention in an equity security market center environment, but it should be understood that the present invention could be used in any type of financial instrument market center environment (e.g., securities, futures contracts, options, bonds, etc.). The trading environment of this embodiment includes a posting market center  20  which interacts with a number of other market centers  24  (i.e. away market centers) and traders  26 . It should be understood that the posting market center  20  referred to herein refers to a computing system having sufficient processing and memory capabilities and does not refer to a specific physical location. In fact, in certain embodiments, the computing system may be distributed over several physical locations. It should also be understood that any number of traders  26  or away market centers  24  can interact with the posting market center  20 . The posting market center  20  is the market center on which a specific trader  26  posts a specific order. The posting market center  20  includes an order matching engine  21 , which validates, matches and processes all orders on the market center  20 . In this embodiment, the order matching engine  21  includes an order maintenance program  22 , which functions to aggressively maintain a market center-restricted order that would normally lock or cross an away market by dynamically re-pricing the order in view of the away market best bid or offer. The order maintenance program  22  may also be utilized as stand alone code separate and apart from the order matching engine  21 . In this embodiment, the code for the order matching engine  21  and for the order maintenance program  22  are stored in the posting market center&#39;s memory. 
     The posting market center  20  may also include a quote and last sale interface  23  that interacts with the away market centers  24  to capture quote and last sale information. This information is stored to a best bids and offers data structure  25 . This data structure  25  is where the Market Best Bid and Offer information is stored. The posting market center  20  may also include an order and trade parameters data structure  27 . The order and trade parameters data structure  27  stores pre-defined trading parameters and rules that are used by the order matching engine  21  in matching orders and executing trades. The posting market center  20  may also include an order and execution interface  28  which interacts with the traders  26 , the away market centers  24  and the order matching engine  21  in the order execution process. The posting market center  20  may also include an order information data structure  29  where order information is stored and a trade information data structure  30  where completed trade information is stored. 
     Throughout the discussion herein, it should be understood that the details regarding the operating environment, data structures, and other technological elements surrounding the posting market center  20  are by way of example and that the present invention may be implemented in various differing forms. For example, the data structures referred to herein may be implemented using any appropriate structure, data storage, or retrieval methodology (e.g., local or remote data storage in data bases, tables, internal arrays, etc.). Furthermore, a market center of the type described herein may support any type of suitable interface on any suitable computer system. 
     Incoming Market Center-Restricted Buy Order 
       FIG. 2  illustrates the process implemented by the order maintenance program  22  where a trader  26  sends a buy order to the posting market center  20  with instructions that the buy order only be executed on the posting market center  20  (i.e. a market center-restricted buy order). At step  100 , a new market center-restricted buy order is received by the order matching engine  21 , and the order matching engine  21 , recognizing the market center restriction, initiates the order maintenance program  22 . At step  102 , the process implemented by the order maintenance program  22  checks to see if the buy order is marketable against the posting market center&#39;s order book. If the buy order is marketable, the process proceeds to step  104  where the order matching engine  21  trades the new buy order against standing orders posted in the posting market center&#39;s order book according to the market center&#39;s trading rules. Then, at step  106 , the process checks to see if the buy order still has any quantity remaining on the order to be traded. If the buy order does not, then the order is complete, and the process ends with respect to this order, as indicated at  108 . If the order is not complete and still has quantity remaining to be traded, the process proceeds to step  112 . Referring back to step  102 , if the incoming buy order is not marketable, the process proceeds to step  112  at this point as well. 
     At step  112 , the process retrieves the away market best offer price from data structure  25 . At step  114 , the away market best offer price is checked to see if it is higher than the buy order price. If the away market best offer price is higher than the buy order price, then the restricted buy order will not lock or cross the away market. The process proceeds to step  116  where a parameter, in this example named TickBack, is set to “N”. Setting TickBack equal to “N” means that the process, as indicated at step  122 , inserts the buy order in the posting market center&#39;s internal book and displays it on the public order book according to normal price/time priority rules for limit orders because the buy order does not lock or cross the away market. 
     Referring back to step  114 , if the process determines that away market best offer price is not higher than the buy order price (i.e. the away market best offer price is equal to or less than the buy order price), then the posting of this order on the posting market center  20  would lock or cross the away market. The process, in this instance, acts to protect the away market centers  24  while not canceling the order, as would have been done with prior systems. The process proceeds to step  123  where the process sets the “Top Price” parameter equal to the price set in the incoming buy order. The Top Price parameter sets the highest possible price that the process will possibly set the order at when pegging it to the away market best offer price. Next, at step  124 , the process computes a tick back price parameter (“Tick Back Price”). The tick back price parameter in this embodiment is equal to the away market best offer price minus one trade increment (i.e. a tick). At step  126 , the process sets the tick back parameter (“Tick Back”) to “Y” so the system knows for later checks that the order price has been ticked back. At step  128 , the process sets a display price parameter (“Display Price”) equal to the Tick Back Price parameter, and at step  130 , the order is inserted into the posting market center&#39;s internal order book and displayed on the public order book according to the price/time priority rules applying to the Display Price parameter, not according to the order&#39;s original higher price (i.e. the Top Price). 
     EXAMPLE 1 
     Incoming Market Center-Restricted Buy Order (Away Market Center at Best Offer Price) 
     An example of a new restricted buy order sent to a posting market center  20  is provided below. It should be understood that the order prices and market prices discussed in this example are by way of example only to illustrate how the process of an embodiment of the invention handles a market center-restricted buy order in a trading environment without a price exemption (i.e. in a trading environment where market best bids and best offers are respected such that orders on one market center are not allowed to trade through an away market center if the away market center is displaying the market best bid or market best offer). 
     In this example, the Market Best Bid is $19.95 and the Market Best Offer is $20.00. An Away Market Center A is quoting 800 @ $ 19.95 to 300 @ $ 20.00. The posting market center  20  has a limit sell order for 300 @ $ 20.01 in the market (Order X). The posting market center internal book in this example appears as follows: 
     
       
         
               
               
             
           
               
                   
               
               
                 Bids 
                 Offers 
               
               
                   
               
             
             
               
                 Away Market Center A 800 
                 Away Market Center A 300 @ 20.00 
               
               
                 @ 19.95 
               
               
                   
                 Order X: 300 @ 20.01 
               
               
                   
               
             
          
         
       
     
     The posting market center  20  receives the three incoming market center-restricted buy orders stated below in the following sequence and processes each order in accordance with the process of  FIG. 2 . 
     Order A: Buy 200 @ $19.99 (lower than the Market Best Offer price) 
     Order B: Buy 600 @ $20.00 (same as the Market Best Offer price) 
     Order C: Buy 700 @ $20.03 (higher than the Market Best Offer price) 
     Order A: 
     For Order A, the market center receives Order A at step  100 . At step  102 , the process assesses Order A&#39;s marketability against the posting market center&#39;s order book. In this case, Order A is not marketable because Order A is priced at $19.99, and this is lower than any offers presently posted on the posting market center  20 . Accordingly, the process proceeds to step  112  where the process gets the away market best offer price from the data structure  25 , which in this example is $20. At step  114 , the process checks whether the away market best offer price is higher than Order A&#39;s buy order price. In this case, the away market best offer price ($20) is higher than Order A&#39;s restricted buy order price ($19.99), so the process continues on to step  116 , setting the TickBack parameter to “N” since Order A&#39;s price does not need to be ticked back. At step  122 , Order A is inserted into the posting market center&#39;s internal order book and is displayed on the public order book as an order to buy at $19.99. 
     Order B: 
     For Order B, the market center receives Order B at step  100 . At step  102 , the process assesses Order B&#39;s marketability against the posting market center&#39;s order book. In this case, as with Order A, Order B is not marketable. Even though Order B is priced at $20 and there is an offer in the market at $20, Order B is a restricted buy order and, as such, cannot execute against the offer at $20 on Away Market Center A. Accordingly, the process proceeds to step  112  where the process gets the away market best offer price of $20 in this example. At step  114 , the process checks whether the away market best offer price is higher than Order B&#39;s buy order price. In this case, the away market best offer price ($20) is not higher than Order B&#39;s restricted buy order price ($20). They are equal. So, the process continues on to step  123 , where the process sets the Top Price to $20 (i.e. Order B&#39;s buy order price). The process, then, at step  124 , computes the tick back price parameter. In this example, the Tick Back Price parameter is $19.99 ($20-$0.01) (i.e. the away market best offer price minus one tick in this embodiment). It should be understood that “one tick” may be any trading increment (e.g., $0.01, $0.02, $0.03, etc.). A tick of $0.01 is used in this example for illustration purposes and in no way limits the scope of the present invention. At step  126 , the process sets the Tick Back parameter to “Y” since Order B&#39;s price needs to be ticked back. At step  128 , the process sets the Display Price parameter equal to the calculated Tick Back Price parameter. In this case, the Display Price parameter is set to $19.99. Then at step  130 , Order B is inserted into the posting market center&#39;s internal order book, and the Display Price parameter of $19.99 is displayed on the public order book. However, the original price (i.e. the Top Price) of $20 is stored on the posting market center&#39;s internal book for reference for potential later re-pricing. 
     Order C: 
     For Order C, the market center receives Order C at step  100 . At step  102 , the process assesses Order C&#39;s marketability against the posting market center&#39;s order book. In this case, as with Orders A and B, Order C is not marketable. Accordingly, the process again proceeds to step  112  where the process gets the away market best offer of $20. At step  114 , the process checks whether the away market best offer price is higher than Order C&#39;s buy order price. In this case, the away market best offer price ($20) is not higher than Order C&#39;s restricted buy order price ($20.03). As such, the process continues on to step  123 , where the process sets the Top Price to $20.03 (i.e. Order C&#39;s buy order price). The process, then, at step  124 , computes the tick back price parameter. In this example, as with Order B, the Tick Back Price parameter is $19.99 ($20-$0.01) (i.e. the away market best offer price minus one tick). At step  126 , the process sets the Tick Back parameter to “Y” since Order C&#39;s price needs to be ticked back. At step  128 , the process sets the Display Price parameter equal to the calculated Tick Back Price parameter. In this case, the Display Price parameter is set to $19.99. Then at step  130 , Order C is inserted into the posting market center&#39;s internal order book, and the Display Price parameter of $19.99 is displayed on the public order book. However, the original price (i.e. the Top Price) of $20.03 is stored on the posting market center&#39;s internal book for reference for potential later re-pricing. 
     After processing Orders A, B and C in this example, the posting market center posts them to its internal book according to price/time priority rules. In this example, the stored parameters appear as follows: 
     
       
         
               
               
             
           
               
                   
               
               
                 Bids 
                 Offers 
               
               
                   
               
             
             
               
                 Order A: 200 @ 19.99, TickBack = N ← 
                 Away Market Center A 300 
               
               
                   
                 @ 20.00 
               
               
                 Order B: 600 @ 19.99, TickBack = Y ← 
                 Order X: 300 @ 20.01 
               
               
                 TopPrice = 20.00 
               
               
                 Order C: 700 @ 19.99, TickBack = Y ← 
               
               
                 TopPrice = 20.03 
               
               
                 Away Market Center A 800 @ 19.95 
               
               
                   
               
             
          
         
       
     
     In this example, at this point, the posting market center&#39;s best bid is 1500 @ $19.99 and the posting market center&#39;s best offer is 300 @ $20.01. The posting market center&#39;s public book looks like this: 
                                 Bids   Offers                   Posting Market Center 1500 @ 19.99   Posting Market Center 300           @ 20.01                    
Update of the Market Best Offer Price and Re-Evaluation of Ticked Back Market Center-Restricted Buy Orders
 
     Once the process has ticked back a market center-restricted buy order, such as Orders B and C in the example above, those orders must be checked and re-evaluated whenever the Market Best Offer price is updated.  FIG. 3  illustrates the process implemented by the order maintenance program  22  where the Market Best Offer price is updated. The order matching engine  21  is continuously checking the best offer price for the entire market. At step  140 , the order matching engine  21  detects a new Market Best Offer price and provides it to the order maintenance program  22 . At step  142 , the process implemented by the order maintenance program  22  retrieves a ticked back restricted buy order that has a “Tick Back” parameter equal to “Y”. At step  144 , the process checks if the posting market center&#39;s best offer price is equal to the Market Best Offer price (i.e. determining whether the posting market center  20  is at the Market Best Offer price). If the posting market center&#39;s best offer price is equal to the Market Best Offer price, then the process proceeds to step  146  where it checks whether the buy order&#39;s Top Price is greater than or equal to the posting market center&#39;s best offer price. If the buy order&#39;s Top Price is greater than or equal to the posting market center&#39;s best offer price, then at step  148 , the process matches the buy order with the sell orders posted in the posting market center&#39;s book. Then, at step  150 , the process checks to see if there is any quantity remaining on the buy order. If not, the process is complete for this order, and it checks to see if there are any further orders with a Tick Back parameter set to “Y”, as indicated at step  172 . If there is quantity remaining on the order, the process, at step  151 , checks to see what the new Market Best Offer price is since the orders that put the posting market center  20  at the Market Best Offer price have now been exhausted. The process then proceeds to step  152 . The process also proceeds to step  152  if the posting market center&#39;s best offer price is not equal to the Market Best Offer price (step  144 ) or if the buy order&#39;s Top Price is less than the posting market center&#39;s best offer price (step  146 ). 
     At step  152 , the process checks if the updated Market Best Offer price is higher than the ticked back market center-restricted buy order&#39;s Display Price. If it is not, then, as indicated at step  154 , the Display Price continues to be posted on the internal order book and displayed on the public order book. In this embodiment, the Display Price will continue to be displayed in the public order book even if, in light of a new away market best offer price, the Away Market Center now crosses or locks the Display Price of the ticked back order on the posting market center  20 . Once a market center-restricted buy order of the present invention is posted, it will stand its ground to later updates of the Market Best Offer price that move to or through the displayed price, even if it results in an Away Market Center price crossing or locking a ticked back order. A market center-restricted buy order of the present invention differs from a traditional buy order that has been pegged to the offer (also known as a Market Peg) in this regard. A traditional pegged buy order moves with the price of the Market Best Offer price in both directions, up and down, even if the price of the Market Best Offer price moves to or through the displayed price of the pegged buy order. A buy order pegged to the Offer does not stand its ground to a Market Best Offer price that moves to or through it, causing the pegged buy order to be re-priced less aggressively. This is in contrast to a market center-restricted buy order of the present invention, which does stand its ground to a Market Best Offer price that moves to or through its displayed price. From step  154 , the process proceeds to step  172  where it checks to see if there are any other buy orders with the Tick Back parameter set to “Y”. 
     Referring back to step  152 , if the updated Market Best Offer price is higher than the ticked back market center-restricted buy order&#39;s Display Price, then the process proceeds to step  156  where the process checks to see if the updated Market Best Offer price is higher than the buy order&#39;s Top Price. If the updated Market Best Offer price is now higher than the buy order&#39;s Top Price, then the buy order&#39;s original price would no longer lock or cross the market if displayed. As such, at step  158 , the TickBack parameter for this order is set to “N”, and this order is no longer a pegged order. At step  160 , the Display Price for this order is set to the Top Price, and at step  162 , the order is inserted into the posting market center&#39;s internal order book and displayed on the public order book according to the price/time priority rules applying to the Display Price parameter, which is now equal to the Top Price. 
     Referring back to step  156 , if the updated Market Best Offer price is not higher than the buy order&#39;s Top Price, then at step  164 , similar to when the order was displayed initially, the process computes a Tick Back Price parameter. As when the order was initially processed, the Tick Back Price parameter in this embodiment is equal to the Market Best Offer price minus one tick. At step  166 , the process sets the Tick Back parameter to “Y” again. At step  168 , the process sets the Display Price parameter equal to the updated Tick Back Price parameter, and at step  162 , the order is inserted into the posting market center&#39;s internal order book and the Display Price is displayed on the public order book according to the price/time priority rules applying to the Display Price parameter, not according to the order&#39;s original higher price (i.e. the Top Price). 
     At step  172 , the process checks to see if there are other buy orders with the Tick Back parameter set to “Y”. If there are, then the process goes back to step  142  and analyzes this order in the same manner it analyzed the previous buy order, as described above. The process continues in this manner until there are no further buy orders with a Tick Back parameter set to “Y” to update, at which point the update is complete as indicated at step  174 . 
     Examples of situations where the away market best offer price has been updated are provided below. It should be understood that the order prices and market prices discussed in these examples are by way of example only to illustrate how the process of an embodiment of the invention handles updating a ticked back market center-restricted buy order. 
     EXAMPLE 2 
     Update of the Market Best Offer Price and Re-Evaluation of Ticked Back Market Center-Restricted Buy Orders (Away Market Best Offer Price Moves Lower; Display Price of Restricted Buy Orders Stand their Ground) 
     In this Example 2, following through from Example 1, the Market Best Offer price has moved lower and has changed from $20 to $19.98. Away Market Center A is now quoting 800 @ $19.95 to 500 @ $19.98. Carrying through from Example 1 above, in the moment before processing and reevaluating the ticked back orders, the posting market center internal book appears as follows: 
     
       
         
               
               
             
           
               
                   
               
               
                 Bids 
                 Offers 
               
               
                   
               
             
             
               
                 Order A: 200 @ 19.99, TickBack = N ← 
                 Away Market Center A 500 
               
               
                   
                 @ 19.98 
               
               
                 Order B: 600 @ 19.99, TickBack = Y ← 
                 Order X: 300 @ 20.01 
               
               
                 TopPrice = 20.00 
               
               
                 Order C: 700 @ 19.99, TickBack = Y ← 
               
               
                 TopPrice = 20.03 
               
               
                 Away Market Center A 800 @ 19.95 
               
               
                   
               
             
          
         
       
     
     Orders B and C, since their Tick Back parameters are set to “Y”, are processed in accordance with the process of  FIG. 3  in light of the updated Market Best Offer price. Due to the similarity of processing in this example, Orders B and C are discussed together, but it should be understood that according to the price/time priority rules in effect that Order B is actually processed first. At step  142 , the process retrieves the order to be analyzed (i.e. in this example, Order B first and then Order C). At step  144 , the process checks to see if the updated posting market center&#39;s best offer price is equal to the Market Best Offer price. In this example, it is not. The process moves on to step  152  where the process determines whether the updated Market Best Offer price is higher than the orders&#39; Display Price. In this example, the updated Market Best Offer price is not higher than Order B and C&#39;s Display Price. Away Market Center A&#39;s ask price is now lower than Order A, B and C&#39;s Display Price ($19.98&lt;$19.99). Therefore, as step  154  indicates, the Display Price for Orders B and C does not change and is not re-priced. Since there are no further ticked back orders with a Tick Back parameter set to “Y”, the update is complete. 
     Orders A, B and C stand their ground even though Away Market Center A has now crossed the posting market center&#39;s order book. In fact, because Orders A, B and C stand their ground, Away Market Center A, according to general marketplace rules applicable in this embodiment of the invention, is required to route an obligation to sell 1500 shares at $19.99 to the posting market center  20 , the displayed size and price on the posting market center  20 . Upon receipt, the posting market center  20  processes this obligation to trade with Orders A, B and C in the same manner it processes all other incoming away market trading obligations, by filling Orders A, B and C. If Away Market Center A does not satisfy its obligation to trade fully against Orders A, B and C, then the posting market center  20  follows its normal procedure of routing a request for satisfaction to Away Market Center A for any shares not filled. 
     EXAMPLE 3 
     Update of the Market Best Offer Price and Re-Evaluation of Ticked Back Market Center-Restricted Buy Orders (Posting Market Center at the Market Best Offer) 
     In this Example 3, following through from Example 1, the Market Best Offer price has moved higher and has changed from $20 to $20.01. The posting market center  20  now has the Market Best Offer (Order X), and Away Market Center A is now quoting 800 @ $19.95 to 400 @ $20.02. Carrying through from Example 1 above, the posting market center internal book in the moment before processing and reevaluating the ticked back orders appears as follows: 
     
       
         
               
               
             
           
               
                   
               
               
                 Bids 
                 Offers 
               
               
                   
               
             
             
               
                 Order A: 200 @ 19.99, TickBack = N ← 
                 Order X: 300 @ 20.01 
               
               
                 Order B: 600 @ 19.99, TickBack = Y ← 
                 Away Market Center A 400 
               
               
                 TopPrice = 20.00 
                 @ 20.02 
               
               
                 Order C: 700 @ 19.99, TickBack = Y ← 
               
               
                 TopPrice = 20.03 
               
               
                 Away Market Center A 800 @ 19.95 
               
               
                   
               
             
          
         
       
     
     Orders B and C, since their Tick Back parameters are set to “Y”, are processed in accordance with the process of  FIG. 3  in light of the updated Market Best Offer price. In this embodiment, Order B is processed first based on price/time priority rules. At step  140 , the market center  20  detects a new Market Best Offer price. At step  142 , the process retrieves Order B, since Order B has a Tick Back parameter set to “Y”. At step  144 , the process checks to see if the posting market center&#39;s best offer price is equal to the Market Best Offer price. In this example, it is. The process moves on to step  146  where the process determines whether the buy order Top Price is greater than or equal to the posting market center&#39;s best offer price. Order B&#39;s Top Price ($20), in this example, is less than the posting market center&#39;s best offer price ($20.01), so the process proceeds to step  152 . At step  152 , the process determines whether the Market Best Offer price is higher than Order B&#39;s Display Price. In this example, the new Market Best Offer price ($20.01) is higher than Order B&#39;s Display Price ($19.99). The process proceeds to step  156  where it determines whether the Market Best Offer price is higher than Order B&#39;s Top Price. In this example, the new Market Best Offer price ($20.01) is higher than Order B&#39;s Top Price ($20). As such, at step  158 , the process sets the Tick Back parameter to “N”, and at step  160  Order B&#39;s Display Price is set to its Top Price since the new Market Best Offer is now higher than Order B&#39;s Top Price. Order B&#39;s Display Price is now set to Order B&#39;s original buy price of $20. Order B is no longer ticked back and will not be re-priced again. At step  162 , the order is inserted into the posting market center&#39;s internal order book and displayed on the public order book according to the price time/priority rules applying to the new Display Price parameter, which is now Order B&#39;s original price. At step  172 , the process checks for other Buy Orders that are ticked back. In this case, it finds Order C. 
     At step  142 , the process retrieves Order C, since Order C has a Tick Back parameter set to “Y” and is next to be processed according to the price/time priority rules applicable in this example. The process then, at step  144 , as before, determines whether the posting market center&#39;s best offer price is equal to the Market Best Offer price. In this example, it still is. Therefore, the process proceeds to step  146  where it determines whether the Order C&#39;s Top Price is greater than or equal to the posting market center&#39;s best offer price. Order C&#39;s Top Price ($20.03), in this example, is greater than the posting market center&#39;s best offer price ($20.01), so the process proceeds to step  148  where the process matches Order C against sell orders posted on the posting market center  20 . In this example, 300 shares of Order C execute against Order X. At step  150 , the process checks to see if Order C has any quantity remaining. In this instance, Order C does. It has 400 shares remaining. The process proceeds to step  151  where it gets the new Market Best Offer price. In this example, the new Market Best Offer price is $20.02 (i.e. the offer of 400 @ 20.02 on Away Market Center A). The process then proceeds to step  152 . 
     At step  152 , the process determines whether the Market Best Offer price is higher than Order C&#39;s Display Price. In this example, the new Market Best Offer price ($20.02) is higher than Order C&#39;s Display Price ($19.99). The process proceeds to step  156  where it determines whether the Market Best Offer price is higher than Order C&#39;s Top Price. In this example, the new Market Best Offer price ($20.02) is not higher than Order C&#39;s Top Price ($20.03). As such, at step  164 , the process computes an updated tick back price parameter. In this example, the Tick Back Price parameter is $20.01 ($20.02-$0.01) (i.e. the away market best offer price minus one tick). At step  166 , the process sets the Tick Back parameter to “Y” since Order C&#39;s price still needs to be ticked back. At step  168 , the process sets the Display Price parameter equal to the calculated Tick Back Price parameter. In this case, the Display Price parameter is set to $20.01. Then at step  162 , Order C is inserted into the posting market center&#39;s internal order book, and the Display Price parameter of $20.01 is displayed on the public order book. However, the original price (i.e. the Top Price) of $20.03 is still stored on the posting market center&#39;s internal book for reference for potential later re-pricing. 
     At step  172 , the process checks to see if there are other buy orders with the Tick Back parameter set to “Y”. There are no more in this example. So, the update is complete, as indicated at step  174 . 
     After processing Orders B and C as explained above, the posting market center posts them to its internal book according to price/time priority rules. In this example, the stored parameters appear as follows: 
     
       
         
               
               
             
           
               
                   
               
               
                 Bids 
                 Offers 
               
               
                   
               
             
             
               
                 Order C: 400 @ 20.01, TickBack = Y ← 
                 Away Market Center A 400 
               
               
                 TopPrice = 20.03 
                 @ 20.02 
               
               
                 Order B: 600 @ 20.00, TickBack = N ← 
               
               
                 TopPrice = 20.00 
               
               
                 Order A: 200 @ 19.99, TickBack = N ← 
               
               
                 Away Market Center A 800 @ 19.95 
               
               
                   
               
             
          
         
       
     
     In this example, at this point, the posting market center&#39;s public book looks like this: 
                                             Bids   Offers                           Posting Market Center 400 @ 20.01               Posting Market Center 600 @ 20.00           Posting Market Center 200 @ 19.99                        
Incoming Market Center-Restricted Sell Order
 
       FIG. 4  illustrates the process implemented by the order maintenance program  22  where a trader  26  sends a sell order to the posting market center  20  with instructions that the sell order only be executed on the posting market center  20  (i.e. a market center-restricted sell order). At step  200 , a new market center-restricted sell order is received by the order matching engine  21 , and the order matching engine  21 , recognizing the market center restriction, initiates the order maintenance program  22 . At step  202 , the process implemented by the order maintenance program  22  checks to see if the sell order is marketable against the posting market center&#39;s order book. If the sell order is marketable, the process proceeds to step  204  where the order matching engine  21  trades the new sell order against standing orders posted in the posting market center&#39;s order book according to the market center&#39;s trading rules. Then, at step  206 , the process checks to see if the sell order still has any quantity remaining on the order to be traded. If the sell order does not, then the order is complete, and the process ends with respect to this order, as indicated at  208 . If the order is not complete and still has quantity remaining to be traded, the process proceeds to step  212 . Referring back to step  202 , if the incoming sell order is not marketable, the process proceeds to step  212  at this point as well. 
     At step  212 , the process retrieves the away market best bid price from data structure  25 . At step  214 , the away market best bid price is checked to see if it is lower than the sell order price. If the away market best bid price is lower than the sell order price, then the restricted sell order will not lock or cross the away market. The process proceeds to step  216  where a parameter, in this example named TickBack, is set to “N”. Setting TickBack equal to “N” means that the process, as indicated at step  222 , inserts the sell order in the posting market center&#39;s internal book and displays it on the public order book according to normal price/time priority rules for limit orders because the sell order does not lock or cross the away market. 
     Referring back to step  214 , if the process determines that away market best bid price is not lower than the sell order price (i.e. the away market best bid price is equal to or greater than the sell order price), then the posting of this order on the posting market center  20  would lock or cross the away market. The process, in this instance, acts to protect the away market centers  24  while not canceling the order, as would have been done with prior systems. The process proceeds to step  223  where the process sets the “Bottom Price” parameter equal to the price set in the incoming sell order. The Bottom Price parameter sets the lowest possible price that the process will possibly set the order at when pegging it to the away market best bid price. Next, at step  224 , the process computes a tick back price parameter (“Tick Back Price”). The tick back price parameter in this embodiment is equal to the away market best bid price plus one trade increment. At step  226 , the process sets the tick back parameter (“Tick Back”) to “Y” so the system knows for later checks that the order price has been ticked back. At step  228 , the process sets a display price parameter (“Display Price”) equal to the Tick Back Price parameter, and at step  230 , the order is inserted into the posting market center&#39;s internal order book and displayed on the public order book according to the price/time priority rules applying to the Display Price parameter, not according to the order&#39;s original lower price (i.e. the Bottom Price). 
     EXAMPLE 4 
     Incoming Market Center-Restricted Sell Order (Away Market Center at Best Bid Price) 
     An example of a new restricted sell order sent to a posting market center  20  is provided below. It should be understood that the order prices and market prices discussed in this example are by way of example only to illustrate how the process of an embodiment of the invention handles a market center-restricted sell order in a trading environment without a price exemption (i.e. in a trading environment where market best bids and best offers are respected such that orders on one market center are not allowed to trade through an away market center if the away market center is displaying the market best bid or market best offer). 
     In this example, the Market Best Bid is $19.95 and the Market Best Offer is $20.00. An Away Market Center A is quoting 300 @ $19.95 to 800 @ $20.00. The posting market center  20  has a limit buy order for 300 @ $19.94 in the market (Order Y). The posting market center internal book in this example appears as follows: 
     
       
         
               
               
             
           
               
                   
               
               
                 Bids 
                 Offers 
               
               
                   
               
             
             
               
                 Away Market Center A 300 @ 19.95 
                 Away Market Center A 800 
               
               
                   
                 @ 20.00 
               
               
                 Order Y: 300 @ 19.94 
               
               
                   
               
             
          
         
       
     
     The posting market center  20  receives the three incoming market center-restricted sell orders stated below in the following sequence and processes each order in accordance with the process of  FIG. 4 . 
     Order D: Sell 200 @ $19.96 (higher than the Market Best Bid price) 
     Order E: Sell 600 @ $19.95 (same as the Market Best Bid price) 
     Order F: Sell 700 @ $19.92 (lower than the Market Best Bid price) 
     Order D: 
     For Order D, the market center receives Order D at step  200 . At step  202 , the process assesses Order D&#39;s marketability against the posting market center&#39;s order book. In this case, Order D is not marketable because Order D is priced at $19.96, and this is higher than any bids presently posted on the posting market center  20 . Accordingly, the process proceeds to step  212  where the process gets the away market best bid price from the data structure  25 , which in this example is $19.95. At step  214 , the process checks whether the away market best bid price is lower than Order D&#39;s sell order price. In this case, the away market best bid price ($19.95) is lower than Order D&#39;s restricted sell order price ($19.96), so the process continues on to step  216 , setting the TickBack parameter to “N” since Order D&#39;s price does not need to be ticked back. At step  222 , Order D is inserted into the posting market center&#39;s internal order book and is displayed on the public order book as an order to sell at $19.96. 
     Order E: 
     For Order E, the market center receives Order E at step  200 . At step  202 , the process assesses Order E&#39;s marketability against the posting market center&#39;s order book. In this case, as with Order D, Order E is not marketable. Even though Order E is priced at $19.95 and there is a bid in the market at $19.95, Order E is a restricted sell order and, as such, cannot execute against the bid at $19.95 on Away Market Center A. Accordingly, the process proceeds to step  212  where the process gets the away market best bid price of $19.95 in this example. At step  214 , the process checks whether the away market best bid price is lower than Order E&#39;s sell order price. In this case, the away market best bid price ($19.95) is not lower than Order E&#39;s restricted sell order price ($19.95). They are equal. So, the process continues on to step  223 , where the process sets the Bottom Price to $19.95 (i.e. Order E&#39;s sell order price). The process, then, at step  224 , computes the tick back price parameter. In this example, the Tick Back Price parameter is $19.96 ($19.95+$0.01) (i.e. the away market best bid price plus one tick in this embodiment). At step  226 , the process sets the Tick Back parameter to “Y” since Order E&#39;s price needs to be ticked back. At step  228 , the process sets the Display Price parameter equal to the calculated Tick Back Price parameter. In this case, the Display Price parameter is set to $19.96. Then at step  230 , Order E is inserted into the posting market center&#39;s internal order book, and the Display Price parameter of $19.96 is displayed on the public order book. However, the original price (i.e. the Bottom Price) of $19.95 is stored on the posting market center&#39;s internal book for reference for potential later re-pricing. 
     Order F: 
     For Order F, the market center receives Order F at step  200 . At step  202 , the process assesses Order F&#39;s marketability against the posting market center&#39;s order book. In this case, as with Orders D and E, Order F is not marketable. Accordingly, the process again proceeds to step  212  where the process gets the away market best bid price of $19.95. At step  214 , the process checks whether the away market best bid price is lower than Order F&#39;s sell order price. In this case, the away market best bid price ($19.95) is not lower than Order F&#39;s restricted sell order price ($19.92). As such, the process continues on to step  223 , where the process sets the Bottom Price to $19.92 (i.e. Order F&#39;s sell order price). The process, then, at step  224 , computes the tick back price parameter. In this example, as with Order E, the Tick Back Price parameter is $19.96 ($19.95+$0.01) (i.e. the away market best bid price plus one tick). At step  226 , the process sets the Tick Back parameter to “Y” since Order F&#39;s price needs to be ticked back. At step  228 , the process sets the Display Price parameter equal to the calculated Tick Back Price parameter. In this case, the Display Price parameter is set to $19.96. Then at step  230 , Order F is inserted into the posting market center&#39;s internal order book, and the Display Price parameter of $19.96 is displayed on the public order book. However, the original price (i.e. the Bottom Price) of $19.92 is stored on the posting market center&#39;s internal book for reference for potential later re-pricing. 
     After processing Orders D, E and F in this example, the posting market center posts them to its internal book according to price/time priority rules. In this example, the stored parameters appear as follows: 
     
       
         
               
               
             
           
               
                   
               
               
                 Bids 
                 Offers 
               
               
                   
               
             
             
               
                 Away Market Center A 300 
                 Order D: 200 @ 19.96, TickBack = N ← 
               
               
                 @ 19.95 
               
               
                 Order Y: 300 @ 19.94 
                 Order E: 600 @ 19.96, TickBack = Y ← 
               
               
                   
                 BottomPrice = 19.95 
               
               
                   
                 Order F: 700 @ 19.96, TickBack = Y ← 
               
               
                   
                 BottomPrice = 19.92 
               
               
                   
                 Away Market Center A 800 @ 20.00 
               
               
                   
               
             
          
         
       
     
     In this example, at this point, the posting market center&#39;s best offer is 1500 @ $19.96 and the posting market center&#39;s best bid is 300 @ $19.94. The posting market center&#39;s public book looks like this: 
                                 Bids   Offers                   Posting Market Center 300 @ 19.94   Posting Market Center 1500           @ 19.96                    
Update of the Market Best Bid Price and Re-Evaluation of Ticked Back Market Center-Restricted Sell Orders
 
     Once the process has ticked back a market center-restricted sell order, such as Orders E and F in the example above, those orders must be checked and re-evaluated whenever the Market Best Bid price is updated.  FIG. 5  illustrates the process implemented by the order maintenance program  22  where the Market Best Bid price is updated. The order matching engine  21  is continuously checking the best bid price for the entire market. At step  240 , the order matching engine  21  detects a new Market Best Bid price and provides it to the order maintenance program  22 . At step  242 , the process implemented by the order maintenance program  22  retrieves a ticked back restricted sell order that has a “Tick Back” parameter equal to “Y”. At step  244 , the process checks if the posting market center&#39;s best bid price is equal to the Market Best Bid price (i.e. determining whether the posting market center  20  is at the Market Best Bid price). If the posting market center&#39;s best bid price is equal to the Market Best Bid price, then the process proceeds to step  246  where it checks whether the sell order&#39;s Bottom Price is less than or equal to the posting market center&#39;s best bid price. If the sell order&#39;s Bottom Price is less than or equal to the posting market center&#39;s best bid price, then at step  248 , the process matches the sell order with the buy orders posted in the posting market center&#39;s book. Then, at step  250 , the process checks to see if there is any quantity remaining on the sell order. If not, the process is complete for this order, and it checks to see if there are any further orders with a Tick Back parameter set to “Y”, as indicated at step  272 . If there is quantity remaining on the order, the process, at step  251 , checks to see what the new Market Best Bid price is since the orders that put the posting market center  20  at the Market Best Bid price have now been exhausted. The process then proceeds to step  252 . The process also proceeds to step  252  if the posting market center&#39;s price is not equal to the Market Best Bid price (step  244 ) or if the sell order&#39;s Bottom Price is greater than the posting market center&#39;s best bid price (step  246 ). 
     At step  252 , the process checks if the updated Market Best Bid price is lower than the ticked back market center-restricted sell order&#39;s Display Price. If it is not, then, as indicated at step  254 , the Display Price continues to be posted on the internal order book and displayed on the public order book. In this embodiment, the Display Price will continue to be displayed in the public order book even if in light of a new away market best bid price, the Away Market Center now crosses or locks the Display Price of the ticked back order on the posting market center  20 . Once a market center-restricted sell order of the present invention is posted, it will stand its ground to later updates of the Market Best Bid price that move to or through the displayed price, even if it results in an Away Market Center price crossing or locking a ticked back order. As with a market center-restricted buy order described above, a market center-restricted sell order of the present invention differs from a traditional sell order that has been pegged to the bid in this regard. A traditional pegged sell order moves with the price on the Market Best Bid price in both directions, up and down, even if the price of the Market Best Bid price moves to or through the displayed price of the pegged sell order. A sell order pegged to the Bid does not stand its ground to a Market Best Bid price that moves to or through it, causing it to be re-priced less aggressively. This, as with the market center-restricted buy order, is in contrast to a market center-restricted sell order of the present invention, which does stand its ground to a Market Best Bid price that moves to or through its displayed price. From step  254 , the process proceeds to step  272  where it checks to see if there are any other sell orders with the Tick Back parameter set to “Y”. 
     Referring back to step  252 , if the updated Market Best Bid price is lower than the ticked back market center-restricted sell order&#39;s Display Price, then the process proceeds to step  256  where the process checks to see if the updated Market Best Bid price is lower than the sell order&#39;s Bottom Price. If the updated Market Best Bid price is now lower than the sell order&#39;s Bottom Price, then the sell order&#39;s original price would no longer lock or cross the market if displayed. As such, at step  258 , the TickBack parameter for this order is set to “N”, and this order is no longer a pegged order. At step  260 , the Display Price for this order is set to the Bottom Price, and at step  262 , the order is inserted into the posting market center&#39;s internal order book and displayed on the public order book according to the price/time priority rules applying to the Display Price parameter, which is now equal to the Bottom Price. 
     Referring back to step  256 , if the updated Market Best Bid price is not lower than the sell order&#39;s Bottom Price, then at step  264 , similar to when the order was displayed initially, the process computes a Tick Back Price parameter. As when the order was initially processed, the Tick Back Price parameter in this embodiment is equal to the Market Best Bid price plus one tick. At step  266 , the process sets the Tick Back parameter to “Y” again. At step  268 , the process sets the Display Price parameter equal to the updated Tick Back Price parameter, and at step  262 , the order is inserted into the posting market center&#39;s internal order book and the Display Price is displayed on the public order book according to the price/time priority rules applying to the Display Price parameter, not according to the order&#39;s original lower price (i.e. the Bottom Price). 
     At step  272 , the process checks to see if there are other sell orders with the Tick Back parameter set to “Y”. If there are, then the process goes back to step  242  and analyzes this order in the same manner it analyzed the previous sell order, as described above. The process continues in this manner until there are no further sell orders with a Tick Back parameter set to “Y” to update, at which point the update is complete as indicated at step  274 . 
     Examples of situations where the away market best bid price has been updated are provided below. It should be understood that the order prices and market prices discussed in these examples are by way of example only to illustrate how the process of an embodiment of the invention handles updating a ticked back market center-restricted sell order. 
     EXAMPLE 5 
     Update of the Market Best Bid Price and Re-Evaluation of Ticked Back Market Center-Restricted Sell Orders (Away Market Best Bid Price Moves Higher; Display Price of Restricted Sell Orders Stand their Ground) 
     In this Example 5, following through from Example 4, the Market Best Bid price has moved higher and has changed from $19.95 to $19.97. Away Market Center A is now quoting 500 @ $19.97 to 800 @ $20. Carrying through from Example 4 above, in the moment before processing and reevaluating the ticked back orders, the posting market center internal book appears as follows: 
     
       
         
               
               
             
           
               
                   
               
               
                 Bids 
                 Offers 
               
               
                   
               
             
             
               
                 Away Market Center A 500 
                 Order D: 200 @ 19.96, TickBack = N ← 
               
               
                 @ 19.97 
               
               
                 Order Y: 300 @ 19.94 
                 Order E: 600 @ 19.96, TickBack = Y ← 
               
               
                   
                 BottomPrice = 19.95 
               
               
                   
                 Order F: 700 @ 19.96, TickBack = Y ← 
               
               
                   
                 BottomPrice = 19.92 
               
               
                   
                 Away Market Center A 800 @ 20.00 
               
               
                   
               
             
          
         
       
     
     Orders E and F, since their Tick Back parameters are set to “Y”, are processed in accordance with the process of  FIG. 5  in light of the updated Market Best Bid price. Due to the similarity of processing in this example, Orders E and F are discussed together, but it should be understood that according to the price/time priority rules in effect that Order E is actually processed first. At step  242 , the process retrieves the order to be analyzed (i.e. in this example, Order E first and then Order F). At step  244 , the process checks to see if the updated posting market center&#39;s best bid price is equal to the Market Best Bid price. In this example, it is not. The process moves on to step  252  where the process determines whether the updated Market Best Bid price is lower than the orders&#39; Display Price. In this example, the updated Market Best Bid price is not lower than Order E and F&#39;s Display Price. Away Market Center A&#39;s bid price is now higher than Order E and F&#39;s Display Price ($19.97&gt;$19.96). Therefore, as step  254  indicates, the Display Price for Orders E and F does not change, and is not re-priced. Since there are no further ticked back orders with a Tick Back parameter set to “Y”, the update is complete. 
     Orders D, E and F stand their ground even though Away Market Center A has now crossed the posting market center&#39;s order book. In fact, because Orders D, E and F stand their ground, Away Market Center A, according to general marketplace rules applicable in this embodiment of the invention, is required to route an obligation to buy 1500 shares at $19.96 to the posting market center  20 , the displayed size and price on the posting market center  20 . Upon receipt, the posting market center  20  processes this obligation to trade with Orders D, E and F in the same manner it processes all other incoming away market trading obligations, by filling Orders D, E and F. If Away Market Center A does not satisfy its obligation to trade fully against Orders D, E and F, then the posting market center  20  follows its normal procedure of routing a request for satisfaction to Away Market Center A for any shares not filled. 
     EXAMPLE 6 
     Update of the Market Best Bid Price and Re-evaluation of Ticked Back Market Center-Restricted Sell Orders (Posting Market Center at the Market Best Bid) 
     In this Example 6, following through from Example 4, the Market Best Bid price has moved lower and has changed from $19.95 to $19.94. The posting market center  20  now has the Market Best Bid (Order Y), and Away Market Center A is now quoting 400 @ $19.93 to 800 @ $20. Carrying through from Example 4 above, the posting market center internal book in the moment before processing and reevaluating the ticked back orders appears as follows: 
     
       
         
               
               
             
           
               
                   
               
               
                 Bids 
                 Offers 
               
               
                   
               
             
             
               
                 Order Y: 300 @ 19.94 
                 Order D: 200 @ 19.96, TickBack = N ← 
               
               
                 Away Market Center A 400 
                 Order E: 600 @ 19.96, TickBack = Y ← 
               
               
                 @ 19.93 
                 BottomPrice = 19.95 
               
               
                   
                 Order F: 700 @ 19.96, TickBack = Y ← 
               
               
                   
                 BottomPrice = 19.92 
               
               
                   
                 Away Market Center A 800 @ 20 
               
               
                   
               
             
          
         
       
     
     Orders E and F, since their Tick Back parameters are set to “Y”, are processed in accordance with the process of  FIG. 5  in light of the updated Market Best Bid price. In this embodiment, Order E is processed first based on price/time priority rules. At step  240 , the market center  20  detects a new Market Best Bid price. At step  242 , the process retrieves Order E, since Order E has a Tick Back parameter set to “Y”. At step  244 , the process checks to see if the posting market center&#39;s best bid price is equal to the Market Best Bid price. In this example, it is. The process moves on to step  246  where the process determines whether the sell order Bottom Price is less than or equal to the posting market center&#39;s best bid price. Order E&#39;s Bottom Price ($19.95), in this example, is greater than the posting market center&#39;s best bid price ($19.94), so the process proceeds to step  252 . At step  252 , the process determines whether the Market Best Bid price is lower than Order E&#39;s Display Price. In this example, the new Market Best Bid price ($19.94) is lower than Order E&#39;s Display Price ($19.96). The process proceeds to step  256  where it determines whether the Market Best Bid price is lower than Order E&#39;s Bottom Price. In this example, the new Market Best Bid price ($19.94) is lower than Order E&#39;s Bottom Price ($19.95). As such, at step  258 , the process sets the Tick Back parameter to “N”, and at step  260  Order E&#39;s Display Price is set to its Bottom Price since the new Market Best Bid is now lower than Order E&#39;s Bottom Price. Order E&#39;s Display Price is now set to Order E&#39;s original buy price of $19.95. Order E is no longer ticked back and will not be re-priced again. At step  262 , the order is inserted into the posting market center&#39;s internal order book and displayed on the public order book according to the price time/priority rules applying to the new Display Price parameter, which is now Order E&#39;s original price. At step  272 , the process checks for other Buy Orders that are ticked back. In this case, it finds Order F. 
     At step  242 , the process retrieves Order F, since Order F has a Tick Back parameter set to “Y” and is next to be processed according to the price/time priority rules applicable in this example. The process then, at step  244 , as before, determines whether the posting market center&#39;s best bid price is equal to the Market Best Bid price. In this example, it still is. Therefore, the process proceeds to step  246  where it determines whether the Order F&#39;s Bottom Price is less than or equal to the posting market center&#39;s best bid price. Order F&#39;s Bottom Price ($19.92), in this example, is less than the posting market center&#39;s best bid price ($19.94), so the process proceeds to step  248  where the process matches Order F against buy orders posted on the posting market center  20 . In this example, 300 shares of Order F execute against Order Y. At step  250 , the process checks to see if Order F has any quantity remaining. In this instance, Order F does. It has 400 shares remaining. The process proceeds to step  251  where it gets the new Market Best Bid price. In this example, the new Market Best Bid price is $19.93 (i.e. the bid of 400 @ 19.93 on Away Market Center A). The process then proceeds to step  252 . 
     At step  252 , the process determines whether the Market Best Bid price is lower than Order F&#39;s Display Price. In this example, the new Market Best Bid price ($19.93) is lower than Order F&#39;s Display Price ($19.96). The process proceeds to step  256  where it determines whether the Market Best Bid price is lower than Order F&#39;s Bottom Price. In this example, the new Market Best Bid price ($19.93) is not lower than Order F&#39;s Bottom Price ($19.92). As such, at step  264 , the process computes an updated tick back price parameter. In this example, the Tick Back Price parameter is $19.94 ($19.93+$0.01) (i.e. the away market best bid price plus one tick). At step  266 , the process sets the Tick Back parameter to “Y” since Order F&#39;s price still needs to be ticked back. At step  268 , the process sets the Display Price parameter equal to the calculated Tick Back Price parameter. In this case, the Display Price parameter is set to $19.94. Then at step  262 , Order F is inserted into the posting market center&#39;s internal order book, and the Display Price parameter of $19.94 is displayed on the public order book. However, the original price (i.e. the Bottom Price) of $19.92 is still stored on the posting market center&#39;s internal book for reference for potential later re-pricing. 
     At step  272 , the process checks to see if there are other sell orders with the Tick Back parameter set to “Y”. There are no more in this example. So, the update is complete, as indicated at step  274 . 
     After processing Orders E and F as explained above, the posting market center posts them to its internal book according to price/time priority rules. In this example, the stored parameters appear as follows: 
     
       
         
               
               
             
           
               
                   
               
               
                 Bids 
                 Offers 
               
               
                   
               
             
             
               
                 Away Market Center A 400 
                 Order F: 400 @ 19.94, TickBack = Y ← 
               
               
                 @ 19.93 
                 BottomPrice = 19.92 
               
               
                   
                 Order E: 600 @ 19.95, TickBack = N ← 
               
               
                   
                 BottomPrice = 19.95 
               
               
                   
                 Order D: 200 @ 19.96, TickBack = N ← 
               
               
                   
                 Away Market Center A 800 @ 20 
               
               
                   
               
             
          
         
       
     
     In this example, at this point, the posting market center&#39;s public book looks like this: 
     
       
         
               
               
               
             
               
               
             
           
               
                   
                   
               
               
                   
                 Bids 
                 Offers 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Posting Market Center 400 @ 19.94 
               
               
                   
                 Posting Market Center 600 @ 19.95 
               
               
                   
                 Posting Market Center 200 @ 19.96 
               
               
                   
                   
               
             
          
         
       
     
     While the invention has been discussed in terms of certain embodiments, it should be appreciated that the invention is not so limited. The embodiments are explained herein by way of example, and there are numerous modifications, variations and other embodiments that may be employed that would still be within the scope of the present invention.