Abstract: The invention is related to a device for determining the position of a structural element to which is affixed a scale composed of regularly spaced markings which are optically cast onto a line scanner containing regularly spaced photosensitive elements, the spacing between photosensitive elements being a subdivision of the distance between two adjacent markings of the scale. The output of the line scanner is coupled to a processing network which detects shifts in the shadows of the cast markings to evaluate the position of the element with precision. A pulse generator in the processing network provides pulses at a frequency which is a multiple of the rate of scanning of the photosensitive elements for measurement of a subdivision of the distance separating two photosensitive elements of the line scanner to obtain greater precision.