A rare, map measurer, used to ascertain distances on geographical maps. This was once an indispensable device used by airmen, motorists, cyclists and hikers etc.
Directions for use: Place the pointer at O by turning the small wheel. Holding the arm of the instrument vertically, trace the distance to be measured with the wheel. The pointer will then indicate on the dial the exact distance in proportion to the scale of the map.
70mm x 35mm, comes in a leather case.