metronome

A device used to mark time by means of regularly recurring ticks or flashes at adjustable intervals.

A mechanical contrivance for marking time, especially as an aid in musical study or performance.

An instrument consisting of a short pendulum with a sliding weight. It is set in motion by clockwork, and serves to measure time in music.

a device, containing an inverted pendulum, used to mark time by means of regular ticks at adjustable intervals; an electronic equivalent that emits flashes

clicking pendulum indicates the exact tempo of a piece of music