An electrodynamometer that may be calibrated as an ammeter, voltmeter, or wattmeter. The signal to be measured produces an electromagnetic torque on the movable coil that in turn is balanced against the torque of a spiral spring connected to it by adjusting a calibrated torsion head attached to the spring. At the balance position the deflection of the movable coil is zero, and the value of the measured parameter is given by the setting of the torsion head.