Abstract: An instrument for measuring sun elevation which includes a structure rotating at a controlled, constant speed. By means of a magnet on said structure a pulse is produced once per revolution. This pulse forms a datum point and can coincide with the horizon. A further pulse is produced by sunlight reflected onto a photo-sensitive device by a mirror rotating with said structure. An oscillator and divider produces a train of pulses, and there is a counter which counts the number of pulses of the train between the datum pulse and the further pulse. As the number of pulses counted is a measure of the time between the further and datum pulses, and this time is a measure of the angle through which said structure has rotated, and this in turn is a measure of the angle between the sun and the horizon, the number of pulses counted can be converted electronically into a read-out of the sun angle.