A method for working out the angular position of a rotating element, by using at least one fixed light source emitting a light beam in the direction of a fixed sensor, arranging the light source with respect to the rotating element and sensor to induce an interaction between the beam and sensor, and providing a value of the angular position dependent of the sensor's output signal. The method including: arranging on the path of the beam a code-disc presenting a two-dimensional pattern of transparent and opaque areas and an absolute code integral with the rotating element, using the image casted by the code-disc on the sensor for determining the eccentricity of the code-disc in dependence of the angular position of the rotating element, using the eccentricity for compensating the value of the computed angular position, and computing a corrected angular position of the rotating element.