pair of compasses

Meaning

A tool for drawing accurate circles or circular arcs, or for measuring or transferring lengths, usually consisting of two arms joined with an adjustable hinge at one end; until the middle ages both arms always had metal points at their free ends (this version is now called a divider or pair of dividers), but in recent centuries for a device called a compass or pair of compasses, one arm typically holds a ruling pen, pencil, or some other implement for making marks.