NYSE on Monday and Tuesday invoked rule 48 to stop panic trading. The rule provides a faster way to open stocks under stressful circumstance by suspending the requirement that stock prices be announced when the market opens thusly ensuring orderly trading when the markets are highly volatile. This preemptive action, invoking rule 48, is what apparently, "tamed the market." http://www.cnbc.com/2015/08/24/rule-48-the-arcane-nyse-rule-to-tame-a-wild-market.html Rule 48 was invoked a few times in recent years, including on Tuesday, January 22, 2008 and on Thursday, May 20, 2010. In 2008, the stock markets were subject to great volatility over fears of a global recession and in 2010, the European debt crisis caused panic buying and selling.
Honestly, I barely understand it other than it is invoked when there is something crazy that happens in Asia or the EU that will cause a crash on the open. But that is mainly for programmed trading. If you know the market is going to crash on open, you would never put an open sell order in, I would only sell above a certain price.
