Just Intonation Strobe Tuner

An electro-mechanical stroboscopic display for visualizing musical sound.  It’s made of a rotating disk with a carefully designed pattern of holes that spins at a precise speed, and a backlight driven by audio input.  If the sound input is at a pitch that synchronizes with the rotation of the disk, a stable pattern emerges.  If it’s slightly sharp or flat, it rotates to the right or left.