Metronome. This device is used by musicians to maintain a steady beat. By raising or lowering the weight (grey), the speed of the beat can be altered. Placing the weight near the top will produce a slow beat (largo), while placing it at the bottom produces a fast beat (presto). This works on the same principle as a pendulum, whose period is determined by the length of the pendulum. Moving the weight essentially lengthens or shortens the pendulum.
