On measures to prevent the programmed trading market fall too far too fast and take another name. After the October 1987 market crash, we have taken many measures to coordinate the relationship between the stock market and the futures market, and at the time of the instability increases, sometimes deliberately breaking the link between the stock market and the futures market. New York Stock Exchange, when the rising or falling 12:00 S & P futures contract, this mechanism came into play, the programmed trading into a special computer to scan the archives buy and sell orders (instructions) in disharmony. This reform allows the New York Stock Exchange stocks in the Dow Jones Industrial Average fell 250 points to stop the operation when one hour; if the same day the index fell 150 points again, can then stop for two hours. Chicago Mercantile Exchange, the S & P 500 futures are not allowed within half an hour the previous day's closing (price) declined by more than 12 points.