The Tektronix 015-0075-00 Video Staircase Differentiator is intended for measuring luminance nonlinearity in analog video systems.
The typical setup for this measurement is as follows: A video signal generator produces a pattern with a few vertical bars with uniformly increasing luminance. The signal is applied to the device or system under test. The output is differentiated by the 015-0075-00 and viewed on an oscilloscope, triggering on the row sync signal.
If the system under test has linear luminance response, the luminance waveform at its output will be a uniform staircase, and differentiating it will produce a series of pulses of equal amplitude. Deviations from linearity, e.g., dynamic compression, will be seen as pulses of decreasing amplitude.