DQ wattmeters are used for active power measurement. There are versions for single-phase AC and three-phase with 3 or 4 wires for balanced and unbalanced loads. The frequency range is 50 – 60 Hz. Ferrodynamic system, with one measuring element for DQ/1w, DQ/1d and DQ/1; two elements for DQ/2 (aron system), and 2 1/2 elements for DQ/3. Eddy-current damping, with pivot suspension and spring-loaded jewel bearings for vibration and shock resistance.