Antique GERMAN Compass OPISOMETER Germany with Leather Case Nautical Map Reading

Description

Working German Opisometer and Compass with original leather case.  Marked Germany, this is for nautical map measuring and converting inches to miles, centimeters to kilometers, etc + has a compass on other side.
An opisometer, also called a curvimeter, meilograph, or map measurer, is an instrument for measuring the lengths of arbitrary curved lines.
The opisometer/compass itself measures 2 7/8 inches long by 1 3/8 inches wide.  The case measures 3 3/8 inches long by 2 1/16 inches wide.
Excellent antique condition. Glass has yellowed a bit. Compass pointer shows a little corrosion, but there are no signs of internal moisture.
See photos for best description.
Thanks for looking!