This pint-sized USB accessory for Windows PCs and Macs is an $80 preview of where man-machine interfaces may be headed. Plug it in, plop it on a flat surface, and you can perform tasks — from playing games to reading New York Times stories — by waving your hands in the air. It can even detect the angle your palms and how many fingers you’re sticking out. The technology is also being built into laptops, starting with HP’s Envy17 Leap Motion SE.
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