High-frequency trading programs make up about half of the trading volume in a normal market day but 70 percent or more on a volatile one. The programs pounce on stock changes to make just slivers of a penny but do it so often that it adds up.

Other investors also use charts and market indicators to make trades based on market momentum. The bet is that if the market is rising, it will keep rising, and if it's falling, it will keep falling.

More investors are turning to this strategy because the sudden slowdown in the economy has left them unable to judge companies based on their fundamentals, like projected profits. The more people use a momentum strategy, the faster the indexes rise or fall....///

more excitement coming soon.. SGX is planning for high-frequency trading programs 

BOSTON (TheStreet) -- S& P Equity Research, whose sister unit downgraded U.S. debt that led to a crash in the stock market Monday, says investors should fall back on tried-and-true measures when buying equities now, given seesawing markets and a weakening economy.

Those gauges ought to include a 10-year record of consistent profit and dividend growth, minimal debt, large amounts of cash, and better cash flow and return on capital than peers, the firm said in announcing its most recent rankings Monday.