A device that can be adjusted to indicate regular beats at any speed within a range that includes all conventional music TEMPOs. The traditional metronome is in a wooden case, pyramidal in shape, standing about 9" in height on a 4"-square base. It is essentially a double pendulum powered by a wind-up spring. The oscillating rod has a weight at each end, the upper one being adjustable along a scale that co-ordinates tempos in beats per minute with the traditional tempo expressions of largo, adagio, moderato, etc. Released, the rod moves from side to side, emitting a loud click with each swing.

This model was invented by Dietrich Winkel of Amsterdam but exploited by, and consequently named after, Johannes Maelzel. Therefore we find on music scores, for example, the indications M.M. = 80, M. = 80 or = 80 to mean: 80 beats (half-NOTEs) per minute on the Maelzel Metronome. More recent models look like a watch and are driven mechanically or by an electric motor. One electric model is a black box less than half the size of a telephone; but along with a repeating sound, a flashing light indicates the beat. See: RHYTHM.

The metronome's original purpose and use was to establish the exact tempo of a piece or section of music. Today, metronomes also perform music, e.g. large groups of pre-set metronomes create polyrhythmic sound textures. Metronomes have also been used in psychological tests dealing with aural perception of patterns and time.