Metronome

tap with the tick. when the lid comes down, keep going.

a wind-up metronome on a piano: tap along with its tick, then its lid slides down and the sound goes; keep the beat in silence, and the lid lifts on the rod where it really is, your drift in ms

A metronome ticks each time its rod passes upright. Tap along and every tap is graded, on the beat, early or late, in milliseconds. Land three in a row and the lid slides down: the rod keeps swinging inside, but you cannot see or hear it, so the beat is yours to keep. Each silent beat you keep inside its window lights a stud on the plinth. Miss the window and the lid flies up on the rod where it really was when you tapped; the red arc from upright is your drift, and the slip shows every silent tap you made, early or late. Keep them all and the weight slides to a new tempo, slower or faster, and the silence gets longer. Every number is your own tap against the card's clock, measured to the frame, about 17 ms.

Concepts: rhythm, timing.

An interactive you play with one thumb, on Wundr.