A power tool includes an electric motor, a functional accessory capable of being driven by the electric motor, a detection device for detecting a rotational speed of the electric motor, and a controller for controlling the electric motor with a control signal. The control is operable to estimate a load parameter according to a duty cycle of the control signal and the rotational speed of the electric motor such that the electric motor is caused to be operated by the controller with a lower rotational speed under a lower load and a higher rotational speed under a higher load.
