Encyclopedia
Metronomes
Metronomes are small mechanical devices used to indicate the precise tempo at which a musical piece should be performed; they are usually enclosed in a box shaped like a pyramid and may be equipped with a bell. The main component is the tempo-indicating pendulum, hinged at its lower end; the movement of the pendulum can be accelerated or slowed according to the scale located behind the pendulum
Source: "Explanations to the Harmonized System of the Russian Federation Customs Tariff (HS RF)" (prepared by the Russian Federal Customs Service) (volume 4, sections XVI - XXI, groups 85 - 97)