I think the black boxes prodominently work on the buy-side, not sell-side. So the drift down is probably an indication of temporary lack of buying , as opposed to a sell program. As a person who used to work in the trading industry, I can say for sure the algarthymic trading programs run wall st. nowadays. A couple years ago, OTC, TSX venture and futures contracts were scarcely infiltrated by the progs; now that has changed. Even exchange is pretty much dominated by them now.
