Quick geek lesson: “persistence of vision” is the optical illusion in which rapidly flashing static images blend together to look like they’re in motion. It’s how films work, and it’s the trick behind Tangram Factory’s Smart Rope ($80), which uses 23 LEDs embedded in the cord to display your jump count in real time in front of you.
“At our office, we took every excuse not to work out—we were too busy, it was raining outside,” says Tangram cofounder Joen Choe. He and his business partner, Deokhee Jeong, wanted an effective fitness routine they could do on the office patio in five minutes. “But if your reps are getting into the hundreds, who wants to count them like a hamster in a wheel?” Choe says.
He promises that the rope’s movement tracker, located in the polycarbonate handles, will never short you on double unders, and thanks to a recent firmware update, the rope now displays calories burned. You can also view your stats on the company’s Smart Gym app (Android and iOS), which hosts Strava-like competitions, leader-boards, and awards.