Reduction compass
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. Use and principle. The reduction compass is made of two branches, with two points each. Several types exist, including the following: The underlying principle is that of proportionality of the sides of two similar isosceles triangles. The reduction compass was customarily used in geography to change the scale of maps.