Analog meter for measuring optical density difference

A device for measuring the difference between the values of the optical density ΔD at two adjacent points of the X-ray picture during the determination of the depth of defect disclosure by the radiographic method is suggested. The measurement is performed by means of a light pen made as a dual-track hollow fork or divider. Each horn of the fork contains a light guide. The ends of the light guides are attached to photomultipliers. Such construction of the pen makes it possible to simplify the techniques of measuring ΔD for any pair of points of the film and to increase the efficiency of measurements