Dow circuit breakers

Just in case you are interested, here are the rules for the New York Stock Exchange Circuit-breakers (from the NYSE website):

CIRCUIT-BREAKER LEVELS
FOR FOURTH-QUARTER 2008
In the event of a 1100-POINT decline in the DJIA (10 percent):
Before 2 p.m. -1-HOUR HALT
2-2:30 p.m. - 30-MIN. HALT
After 2:30 p.m. -NO HALT

In the event of a 2200-POINT decline in the DJIA (20 percent):
Before 1 p.m. - 2-HOUR HALT
1-2 p.m. - 1-HOUR HALT
After 2 p.m. --MARKET CLOSES

In the event of a 3350-POINT decline in the DJIA (30 percent), regardless of the time, MARKET CLOSES for the day.

NYSE Circuit Breakers
In response to the market breaks in October 1987 and October 1989 the New York Stock Exchange instituted circuit breakers to reduce volatility and promote investor confidence. By implementing a pause in trading, investors are given time to assimilate incoming information and the ability to make informed choices during periods of high market volatility.

Rule 80B
Effective April 15, 1998 the SEC approved amendments to Rule 80B (Trading Halts Due to Extraordinary Market Volatility) which revised the halt provisions and the circuit-breaker levels. The trigger levels for a market-wide trading halt were set at 10%, 20% and 30% of the DJIA, calculated at the beginning of each calendar quarter, using the average closing value of the DJIA for the prior month, thereby establishing specific point values for the quarter. Each trigger value is rounded to the nearest 50 points.

The halt for a 10% decline would be one hour if it occurred before 2 p.m., and for 30 minutes if it occurred between 2 and 2:30, but would not halt trading at all after 2:30. The halt for a 20% decline would be two hours if it occurred before 1 p.m., and between 1 p.m. and 2 p.m. for one hour, and close the market for the rest of the day after 2 p.m. If the market declined by 30%, at any time, trading would be halted for the remainder of the day.

Under the previous Rule 80B trigger points (in effect since October 19, 1988) for a market-wide trading halt, a decline of 350 points in the DJIA would halt trading for 30 minutes and a drop of 550 points one hour. These trigger points were hit only once on October 27, 1997, when the DJIA was down 350 at 2:35 p.m. and 550 at 3:30, shutting the market for the remainder of the day.