A metronome is a device that produces an audible click or other sound at a uniform interval that can be set by the user, typically in beats per minute (BPM). Metronomes may also include synchronized visual motion, such as a swinging pendulum or a blinking light. Musicians—and others including dancers, athletes, and health professionals—often practise with a metronome to improve their timing, especially the ability to maintain a steady tempo with a regular beat or pulse. Composers and conductors often use numerical metronome markings to communicate their preferred tempos to musicians preparing for a performance.
Maelzel's Metronome
Franz eletromechanical metronome
Wittner electronic metronome
In musical terminology, tempo, also known as beats per minute, is the speed or pace of a given composition. In classical music, tempo is typically indicated with an instruction at the start of a piece and is usually measured in beats per minute (BPM). In modern classical compositions, a "metronome mark" in beats per minute may supplement or replace the normal tempo marking, while in modern genres like electronic dance music, tempo will typically simply be stated in BPM.
Wittner electronic metronome