I got it. =) see below: Most exchanges follow a "price-time priority" principle for both orders and quotes. Whenever an order is placed at any exchange, it's given a timestamp which is then used to prioritize your orders. This method of trading is called Central Limit Order Book or "CLOB" and is used by most exchanges globally. Such a system is necessary to maintain transparency in matching customer orders (bids and offers) on a "price-time priority" basis. The highest bid will be matched against the lowest offer. The global standard also demands that the best 5 bids/offers be visible to all market participants by way of Snap Quote.