An instrument that measures electric power and is calibrated in watts, multiples of a watt, or submultiples of a watt. The most commonly used type of wattmeter is the electrodynamic wattmeter (see electrodynamometer). In circuits that have substantially constant currents and voltages an induction wattmeter (see induction instrument) may be used. For standardization and calibration purposes an electrostatic wattmeter is used. This consists of a quadrant electrometer that is arranged in a suitable circuit containing noninductive resistors so that it measures power directly.