"Map-Mate Map Counter" - an electronic odometer to roll over map to measure distance, electronic so can do calculations of speed too (must have internal clock). And works as straight forward calculator.
Includes a little separate compass.
These can still be bought (https://www.amazon.com/Map-Mate-Electronic-Measuring-Tool/dp/B00404I5OK) but I haven't had any luck finding instructions on-line.
New battery.
Calculator function works.