Grafikon CRT monitor greyscale setting instrument. Old device but still works.
The instrument is marked on the outside as the foam support in the case has disintegrated completely and stuck to it.
The iris system still operates controlling the light level of the area around the central spot. tweak the iris to match the greyscale step and adjust the colour balance so it's invisible.
It's an antique and a museum piece so a bit rough but I can't throw it away.