A contour plotter has been designed to display the sensitivity uniformity of photocathodes in quantized format on the Z axis of an oscilloscope. An optical scanner, synchronously driven by the oscilloscope X‐Y deflection signals is used to raster scan the photocathode with a focused light beam. Sensitivity, resolution, and scanning time are sufficient to use the plotter to monitor sequential processing steps for photocathodes in demountable, ultrahigh vacuum systems. A general description of the contour plotter system and a detailed circuit description are given. An example relating to cesium uniformity on a III‐V photocathode is presented to illustrate the use of the contour plotter.