Compass, divider, and caliper are basically instruments that have two legs pivoted to each other at the top and are concerned with small-distance measurement or transfer. The compass and divider have straight legs; the caliper has curved legs.

The terms compass and divider are often interchanged, for each instrument can be used to draw circles, mark divisions (divide a given distance), or simply mark a distance.

A pair of compasses, also known as a compass, is a technical drawing instrument that can be used for inscribing circles or arcs. Compasses can be used for mathematics, drafting, navigation and other purposes.

Compasses are usually made of metal or plastic, and consist of two parts connected by a hinge which can be adjusted to allow the changing of the radius of the circle drawn. Typically one part has a spike at its end, and the other part a pencil, or sometimes a pen.

Prior to computerization, compasses and other tools for manual drafting were often packaged as a "bow set" with interchangeable parts. By the mid-twentieth century, circle templates supplemented the use of compasses.

Today these facilities are more often provided by computer-aided design programs, so the physical tools serve mainly a didactic purpose in teaching geometry, technical drawing, etc.

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