A German Nautical what?! Simply put, an opisometer is a tool used to measure the length of curved lines, particularly on maps. Also called a curvimeter, a meilograph, and a map measurer. It consists of a toothed wheel on a handle that is rolled along a curved line, moving the pointer on a scale that indicates the distance traveled. Pretty groovy, eh? This opisometer includes a compass on one side and measures 4-3/4" long. It's in excellent condition and would be a first-rate addition to any collection.