What adjustable measuring instrument did Leonardo da Vinci design for comparing distances and proportions?

Leonardo da Vinci designed a proportional compass for comparing distances and proportions.

A proportional compass has two arms joined by a movable pivot. By changing the pivot’s position, a user can transfer or enlarge a measurement according to a chosen ratio. This made the instrument useful for geometry, drawing, architecture, surveying, and mechanical design.

Unlike a magnetic compass, the proportional compass does not find north. It is also different from a simple pair of dividers, which transfers measurements without automatically applying a selectable scale. Leonardo’s version reflects his habit of combining mathematical geometry with practical workshop tools.

Leonardo was not the only Renaissance figure interested in proportional instruments, and later makers developed more standardized versions. The device is therefore best understood as part of the development of proportional compasses rather than as a modern precision instrument identical to those used today.