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Alex Barnett takes a small silver tuning fork from his backpack, thwacks it against his desk and holds it to a microphone. On his computer, the musical tone appears as a steady succession of identical sine waves.

“It’s an A4, or the A above middle C,” says Barnett, who plays classical and jazz piano in addition to serving as group leader for numerical analysis at the Flatiron Institute’s Center for Computational Mathematics (CCM). “That’s 440 hertz, or 440 oscillations per second.”