Stocks are tumbling to start a new month of trading, as technology names struggle and new economic data rekindles fears around the health of the economy. The Dow is down 1.5%, the S&P 500 is down 2% and the Nasdaq Composite is down more than 3%, putting the tech-heavy index on pace for its worst day since Aug. 5′s global market rout. We’ll tell you all you need to know today.