The New York Stock Exchange invoked a special rule today in an effort to smooth volatility and trading at the market open, reports Reuters.

Rule 48 says that when the NYSE finds “an extreme market volatility condition with respect to trading on or through the facilities of the Exchange,” market makers do not have to provide price indications before open. That makes it “easier and faster to open stocks,” says the Wall Street Journal in an explainer. “The rule was approved by the Securities and Exchange Commission on Dec. 6, 2007.” The rule was last used in January 2015.

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Monday’s open saw the S&P 500 drop more than 4%, but as of 11:10 am, it was down just 2.9%. Other indices saw similar activity: The S&P/TSX Composite fell 700 points in early trading, but as of 11:10 am, it was down 310 points or 2.3%. The Dow fell 1,000 points at open, but was down 460 points (2.8%) by 11:10 am.