Reuters: "For the current quarter, circuit breakers will kick in if there is a drop of 1,350 points, or 10 percent, in the Dow Jones industrial average.

"There will be a one-hour halt in trading if the drop happens before 2 p.m., a 30-minute halt if the decline occurs between 2 p.m. and 2.30 p.m., and no halt after 2.30 p.m., according to the NYSE.

"If the Dow drops 2,700 points or 20 percent, there will be a two-hour halt if it happens before 1 p.m., a one-hour halt if the slide occurs between 1 p.m. and 2 p.m. and the market will close if the slide happens after 2 p.m.

"A plunge of 4,050 points or 30 percent -- regardless of the time it occurs -- would result in the market being closed for the day." (Thanks to Charles Everett)