August,
I don't want to go digging through all the posts to find that stuff for you (too much on-line time today already, and relatives on their way over ;) but ARCA is excellent for building large positions. Say you want to buy WXYZ and it is getting hammered down a little on an intraday pullback, trading 17 3/4 by 17 15/16. There are shares coming across the tape both sides of the market but the momentum has been downward (and is about to turn up). At that momement you'd stick in an ARCA bid in for 10,000 shares at 17 3/4 or 17 13/16. It will just set there persistently and suck them down as your bid gets hit by sellers. Theoretically you can do that with ISLD, but I find that in reality the ISLD order will cancel after they hit you with the first lot or two (then, you get into re-entering the order, and multiple commissions). ARCA, on the other hand, goes out and aggressively works different Selectnet order modes for you to get your entire order filled. So often on ISLD you'll end up with cancellation of the order after a partial fill, and multiple tickets. Nowadays, though with the excellent visibility into the ISLD book, you can usually get the job done on ISLD by viewing the book then placing the order properly, which is generally much faster. Hope that helps,
-Steve |
