 This is the VOA Special English Economics Report. Once, stocks were traded through the open outcry system. Today, fast interconnected computers have mostly replaced the trader's shouting prices on the floors of stock exchanges. Joe Saluzzi is a head of equity trading at Themis Trading in New Jersey. The equity market has changed. It's no longer what you see on TV. It's no longer guys with colored jackets running around the floor anymore. The equity market is a bunch of co-located computers strung together by a bunch of wires, everyone trying to race to zero. The speed of light is the goal. Traders can process stock trades in thousands of a second. Andrew Haynes of Gain Capital is an online broker. A millisecond can mean millions of dollars to the success of your strategy. Having a one, two, three millisecond advantage over other traders may mean that you get into a trade at a preferable price. Andrew Haynes says an estimated 70% of all stock trades are high-frequency trades made with complex computer models. Stocks may be held for only seconds. But fast trades are also blamed for big moves in stock prices. On May 6, 2010, a leading measure of American stocks briefly fell about 9%. The Dow Jones industrial average then recovered much of those losses by the end of trading that day. The Securities and Exchange Commission ordered steps to prevent future flash crashes like that one. Joel Hasbrook of New York University says those steps are working. They're called circuit breakers, and basically what they mean is that when a stock has moved by a large amount in a short period of time, there's a trading halt. Joe Saluzzi of Femus Trading says the main problem with high-speed trading is an unbalanced market. The stock market used to be a predictor of the future economy. Now, I think the stock market is a backwards predictor. It's forecasting the next microsecond move. It's not forecasting the next six months because most of the volume is being dominated by guys who could care less what goes on in six months. So how could you think the price is being set correctly? But Joel Hasbrook says high-speed trading can reduce sharp rises or drops in stock prices. In normal circumstances, high-frequency traders act as market makers. That means they stand by passively waiting to buy or sell from whoever comes into the market needing to trade. In that capacity, they actually help stabilize the market. For VOA Special English, I'm Alex Villareal.