Abstract: A light source throws a light beam through a transparent scale provided with graduation lines. The light beam is focussed by means of an aperture in such a way that it is disposed at an inclined angle with respect to the graduation lines. Upon relative displacement as between the scale and the aperture, that arrangement provides that a constantly changing light beam is projected onto a photosensitive receiving means. Depending on the respective position and configuration of the light beam on the receiving means, it is possible to arrive at the relative position of the scale within a travel increment.