they have a "patented" computer trading program that they have had for a long time. HSX has never said if it takes 1M shares to make a stock price move, or only 100 shares.
I can tell you this, though... I've seen the price move on a BIG priced stock when I've bought 100K shares of it, and then again... I've seen the price NOT rise on other stocks when I've done the same thing. So there is something in their software program that analyzes trading somehow, and then adjusts (or doesn't adjust) the price when shares are bought or sold.
HSX of course, sells the data they collect from this software program.. here's what they say about it:
The Company's Virtual Specialist® technology allows an unlimited number of consumers to trade thousands of virtual entertainment securities in a fair and orderly, supply-and-demand-based market. HSX syndicates the data collected from the Exchange as market research to entertainment, consumer product and financial institutions and as original content to radio, television and print media.
Anyway, it's a trade secret...and HSX ain't tellin'. 