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On an exchange, a measure designed to prevent panic selling by stopping trading after a security or an index has fallen by a certain amount. For example, if the Dow Jones Industrial Average falls 10% in a trading day, the New York Stock Exchange institutes a trading curb that suspends trade for at least one hour. A trading curb is intended to allow investors to determine whether a situation is really as bad as it looks. It is sometimes called a collar or a circuit breaker. See also: Suspended trading.