Opisometer vs. Curvimeter — What's the Difference?

An opisometer, also called a curvimeter, meilograph, or map measurer, is an instrument for measuring the lengths of arbitrary curved lines. A simple opisometer consists of a toothed wheel of known circumference on a handle.

A device for measuring the length of curves, such as on a map

A device for measuring the length of curved lines, such as on a map.

An instrument with a revolving wheel for measuring a curved line, as on a map.