Winkelmesser W.M.35 German Artillery and Mortar Level

Original German artillery and mortar winkelmesser W.M.35 in the original box with the original key. There is always a small flat unpainted area on nearly every piece of German artillery near the breach, that is where this would be placed and clamped down. This would allow you to calibrate the mounting of the sight block. This seems to me like it was possibly a very well preserved ground or bog find. It has clearly been cleaned up a bit and while it is not currently rusty, it looks like it was fairly rusty at some point. The glass bubble level is also in good working condition.