Carl Zeiss Jena - 1948

This is a device that I do know how to call it in english? But this has been what my late grand father has used in planning roads to north Finland after the war years (late 1940s). You can measure the elevation of the ground level with this. Can't find the right words for it :) but it is the same Carl Zeiss company that made this device to be used at 1948 that makes high quality optics still today.