There are various methods of calculating the engine displacement of a Wankel. The Japanese regulations for calculating displacements for engine ratings use the volume displacement of one rotor face only, and the auto industry commonly accepts this method as the standard for calculating the displacement of a rotary. When compared by specific output, however, the convention resulted in large imbalances in favor of the Wankel motor. An early revised approach was to rate the displacement of each rotor as two times the chamber.