On New Year's Day, NYSE Euronext (NYSE:NYX.DL) announced its quarterly changes to the circuit-breaker triggers. These are safeguards against market panics that would put a temporary stop to NYSE trading if the Dow Jones Industrial Average (DJINDICES:^DJI) fell too far, too fast.

The trigger levels have generally stabilized over the last year, in concert with the Dow's overall direction:


Q1 2012
Trigger Levels

Q4 2012
Trigger Levels

Q1 2013
Trigger Levels

Level 1 Halt (generally a 1-hour trading pause)

-1,200 points

-1,350 points

-1,300 points

Level 2 Halt (generally a 2-hour trading pause)

-2,400 points

-2,700 points

-2.650 points

Level 3 Halt (no more trading that day)

-3,600 points

-4,050 points

-3,950 points

Source: NYSE press releases.

But this update came with a surprise: The NYSE will switch its trigger calculations trom the Dow to the broader S&P 500 (SNPINDEX:^GSPC) index on Feb. 4.

The exchange did not say what brought on this sudden and previously unannounced change in philosophy. Both the Dow and S&P 500 indexes are managed under the S&P/Dow Jones Indices umbrella, which is a joint venture between Dow Jones owner CME Group (NASDAQ:CME) and S&P manager McGraw-Hill (NYSE:SPGI).

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