The reduction compass or proportional dividers is a geometry tool with asymmetric-length branches to allow performing homothetic transformations, reproducing a pattern while enlarging or reducing its size and conserving angles. It was invented by Fabrizio Mordente before 1567.[1]
Use and principle
The reduction compass is made of two branches, with two points each. Several types exist, including the following:
simple reduction compass: the pivot is fixed, and the enlargement factor is determined by the length difference between the small and long end of the branches;
mobile-headed reduction compass: the pivot is mounted on a slide, and its position determines the enlargement factor.[2]