A device and a method may be used to determine a highly accurate absolute angle of rotation Xt of the rotational position of a rotatably supported steering shaft. Rotation of a rotor of an electric motor with a gearing with a gearing transmission factor K for power assistance may be coupled into rotation of the steering shaft. A rotational position of rotation of the rotor can be measured by means of a rotor position sensor and by using a number of revolutions of the rotor that have occurred. This value is used directly to determine the highly accurate absolute angle of rotation Xt of the steering shaft. Calibration methods involve determining initial values from which the counting of revolutions or the calculations occur.