Dynamometer (aka rolling-road, dyno or Leistungpruefstand) is a mechanical device for measuring power and torque of a car, bike, truck or even an agricultural machine. The torque produced by an engine is converted to traction force by transmission (gearbox, differential) at wheels. You may ask – where is the place for „power” then? Power is the torque of the engine multiplied by the rotation speed – so it is enough to measure traction force to be able to calculate the wheel power of a car, truck, motorbike. Of course our dynamometer must know noticeably more to show us the real power of the engine – power losses must be measured, also the dyno must know the transmission ratio (wheel speed to engine speed ratio) or directly the engine speed (for instance – from OBD port or CANBUS of the car).