Ww2 pre-war map measuring device, vernier measuring device, cross table with vernier scale
A measuring device for determining a length is called a vernier. The special thing about a vernier is that two length scales are combined, one of which can be moved to record the exact dimensions. The two scales allow you to read the value much more precisely than with a conventional length scale. Scale 1: 2000 and 1: 2500
The device was produced before the war, used in a wartime manner and was last used / tested in the 1950s