A meter movement can be equipped with a marking device to keep a graphic record of the level of some quantity with respect to time. Such a device is called a pen recorder. The paper, with a calibrated scale, is taped to a rotating drum. The drum, driven by a clock motor, turns at a slow rate, such as one revolution per hour or one revolution in 24 hours. A simplified drawing of a pen recorder is shown in Figure :
A functional drawing of a pen recorder.
A device of this kind, along with a wattmeter, can be employed to get a reading of the power consumed by your household at various times during the day. In this way you can find out when you use the most power, and at what particular times you might be using too much.