quartz metronome
Metronome that translates the electric signal produced by a piece of quartz into sound or visual signals.
sound signal 
Device that translates the metronome’s electric signal into beeps; its volume can be controlled.
standard A 
Reference note established as the international standard; its frequency is 440 Hz (440 vibrations per second).
light signal 
Part that translates the electronic beats of the metronome into flashing light.