Though investors have endured some pretty terrible Dow performances in recent weeks, including another 300-plus point on Friday, the downward spiral has not gone far enough to halt trading on Wall Street.

New York Stock Exchange rules currently call for circuit breakers to interrupt trading only in cases of extreme drops of more than 1,100 points. Such breaks, established after the Black Monday crash in 1987, are intended to help investors step back and assess what is happening.

The thresholds for market timeouts are set quarterly, using the Dow’s average closing price for the previous month, and activate in increments of 10, 20, and 30 percentage point drops.

For the current fourth quarter, if the Dow drops 1,100 points before 2 p.m., trading stops for an hour. If such a drop happens between 2 p.m. and 2:30 p.m., trading halts for a half hour. After 2:30 p.m., the 1,100-point threshold expires.

There is also a 2,200-point mark. If the Dow falls by that much before 1 p.m., trading stops for two hours. Between 1 p.m. and 2 p.m., a 2,200-drop causes an hour halt. After 2 p.m., trading ends.

If the Dow falls by 3,350 points, trading stops for the rest of the day.

The circuit breakers have been activated twice, both times in late afternoon trading on Oct. 27, 1997, when the Dow eventually closed off 554 points, or 7.2 percent. Trading that day was halted under previous triggers, which were later revised in 1998. The current triggers have never been hit.
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