Wehrmacht 'Deckungswinkelmesser'. The 'Deckungswinkelmesser' was stored in a small pocket inside the standard leather map case, it was used to calculate distances and height differences in terrain. Complete with aluminum instruction plate. It's nicely maker marked with 'Jdem' indicating production by the company of 'J.D. Möller G.m.b.H.' from Wedel. Hard to find original example in good used condition. Nice item to complete your map case with!