Another use for a metronome is for a gradual increase in tempo. The increments are so small that almost without knowing it, the student increases the speed at which she can play the piece accurately. Many teachers use the metronome as an adjunct to technical drills. These are the wind-up kind and work by a spring mechanism. When the spring unwinds entirely, the metronome stops and must be re-wound.
Speed is changed by moving a weight on a pendulum-type arm.
The closer the kids sit to the fulcrum, the faster the movement. A mechanical metronome is sort of half of a teeter-totter. The moveable weight is one child, and the unmoveable counterweight is the other child. It is possible to get smaller ones, too, that do not take up a lot of room on the piano. This type is sensitive to being dropped or the weights in the moving arm otherwise disturbed.