Abstract: A machine for measuring the size of objects that are in motion in single file includes in one embodiment a collimated light beam that as a narrow horizontal width and a long vertical width. The light beam is pulsed ON and OFF at a 10 kilohertz rate but with the light being turned on only 30 percent of the time. The maximum shadow is cast by the maximum height of the object, and causes a minimum oputput voltage amplitude from a photodetector. This minimum output voltage is compared with a reference voltage to determine the object size. A direct digital readout may be obtained. Also, the size information may be passed to a microprocessor or similar device for use in sorting operations. In another embodiment a pair of collimated light beams are positioned about an aperture such that the beams are othogonal. An object passing through the aperture causes a loss of light to each photodetector. The voltage output of each photodetector is combined and averaged.