Apple Tumbles as Much as Six Percent in What Looks Like Robot Trading | Re/code

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"The stock lost over three percent in that minute, falling as much as 6.4 percent to $111.27. At midday, it was down three percent to $115.40.

The cause of the decline was not yet clear, though traders pointed to high-speed algorithmic trading programs as a potential culprit. Steve Hammer, a trading educator and founder of HFT Alert in Santa Barbara, Calif., which monitors algorithmic trading, said about 300 different stocks showed elevated price traffic beginning about 9:50 am ET, a sign of institutions putting on sell programs.

“When you see that kind of price action that is simply algos running stocks,” he said."

Apple Tumbles as Much as Six Percent in What Looks Like Robot Trading | Re/code