Abstract: An electro-optical gaging system which comprises a linear array of photo-sensitive diodes where the thickness of an object against a dark background is measured by determining the number of diodes which are discharged due to light incident thereon from the object. Each diode of the array is sequentially scanned during a scanning cycle to recharge the capacitance of the discharged diodes and the number of charging pulses is a measurement of the thickness of the object. A separate photo-sensitive element senses the light conditions and generates pulses which determine the repetition rate of the scanning cycle to maintain system calibration. A start scan signal is also utilized to determine that the light intensity is within predetermined limits.