How the NYSE's market 'circuit breakers' would work

The New York Stock Exchange has "circuit breakers" in place that are designed to temporarily halt trading in the event of a market freefall.

But it would take a lot more than the current 547-point drop in the Dow Jones industrials (as of 12:15 p.m. PDT) to trigger the circuit breakers.

Here are the rules:

--- If the Dow falls 1,100 points before 11 a.m. PDT, trading is halted for one hour.

--- If the Dow falls 1,100 points between 11 a.m. and 11:30 a.m. PDT, trading is halted for 30 minutes.

--- After 11:30 a.m. PDT (with 90 minutes left in the trading day), the Dow could continue to decline past 1,100 points and no halt would be called until it fell 2,200 points.

--- A Dow drop of 2,200 points any time after 11 a.m. would close the markets for the rest of the day.

The circuit breakers are reset each quarter. The 1,100-point threshold for the first circuit breaker equates to a 10% drop in the Dow -- or, rather, to what would have been a 10% drop based on where the Dow ended the previous quarter.

The Dow was down as much as 800 points before noon, still far from the 1,100-point trigger for the first circuit breaker.