Program Trading "Collars" 
A collar on program trading firms instituted by the NYSE is most commonly referred to on CNBC as "NYSE Trading Curbs".  The Exchange
applies program trading curbs whenever the Dow Jones Industrial Average moves 50 points higher, or 50 points lower than the previous dayıs
closing price. 

The NYSE restriction on program trades stays in place until the Dow Jones returns to within 25 points of the previous dayıs closing price; or, until the end of the trading day at 3:00 CT.  NYSE Trading Curbs apply only to our firm's (and other program trading firm's) computer assisted program trades. 

The NYSE defines a Program Trade as: 
  1.  A basket of 15 or more stocks from the Standard & Poorıs 500 Index. 
  2.  A basket of stocks from the Standard & Poor's 500 Index valued at $1 million or more. 

Once the NYSE program trading collar is in place, Program Selling can be executed only on an up-tick.  That means that the last trade was
executed at a higher price than the trade before it. 
Program Buying can be executed only on a down-tick. That means that the last trade was executed at a lower price than the trade before it. 

Program Trading "Sidecars" 
This is another type of NYSE Trading Curb.  The NYSE applies this program trading curb whenever the S&P 500 Futures Contract, traded on the Chicago Mercantile Exchange, moves 12 points above or below the current trading dayıs opening level (8:30 AM CT).   This restriction on
program trading firms requires all program trades to be held for at least five minutes.  PLUS, after five minutes, all program selling or program buying must be executed only if it can be done without causing the market to go up or down.  A 12 point move in the S&P 500 Futures Contract is equivalent to a move of about 95 points in the Dow Jones Industrial Average. 

Program Trading "Circuit Breakers" 
If the Dow Jones Industrial Average falls 350 points, trading is halted on the New York Stock Exchange for 30 minutes.  If the Dow Jones rallies
350 points, there is no restriction.  Why?  Because program buying and the accompany rally is always perceived as "good". 

If the Dow Jones Industrial Average falls 550 points, trading is halted on the New York Stock Exchange for one hour. There is no trading halt if it rallies 550 points, as that would be perceived as "very very good". 

Recently the NYSE made a few changes to the above:  After 2 p.m., the 550-point circuit breaker would trigger a 30-minute halt, instead of a 60-minute halt. Trading would not resume if the 550-point threshold was triggered after 3 p.m.  After 3 p.m., the 350-point circuit breaker would be removed, allowing trading to continue uninterrupted until the 550-point threshold.