The distinguishing feature of PSX is that it allows for any "pro rata" priority at all -- other US equities markets follow a price-time priority only (aside from the fact that a few exchanges such as NYSE that allow "special" firms, "DMM's" on NYSE, to cut the queue). In other words, with PSX, you can match the bid/offer and then get some allocation of any incoming order, as per the formula on the Web page you list. On the MOST other exchanges, the FIRST person at the best price gets fully filled first, followed by the next in the queue at that same price, etc., until everyone at the price has been filled.BTW, can someone explain in simple terms how priority works on PSX (http://www.nasdaqtrader.com/Trader.aspx?id=nasdaqpsx) ?
They keep saying "price setter," but I have no idea what that means. If you are showing the best price on a given exchange (no one is at the same level as you are), of course you get filled first -- so that can't be it. If it's that you are the first to post at a given price and others then join you, that's simple time-priority, so that can't be it either.
I'm pretty sure what they mean by "price setter" is the FIRST best bid/offer for that price on the PSX -- on most other exchanges, the "price setter" gets 100% of incoming orders (up to the point of the size of their order, of course).
PSX hasn't been particularly successful with this model, and that probably has something to do with the fact that the market is highly fragmented anyway.
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