Not sure of its age, maybe from the 60s?  Beautifully built with leather case. 

One side is a compass. The other side is a measurer / unit converter. Rolling it along a map will cause the needle to climb. 1" = 1 mile. You can measure distances on a map very quickly with this. The card has miles, kilometers, and nautical miles so you can also convert the units displayed under the needle easily.