- Use and principle
{{short description|}}The reduction compass or proportional dividers is a geometry tool with asymetric-length branched, as to allow performing homothetic transformations, that is reproducing a pattern while enlarging or reducing its size and conserving angles. Use and principle The reduction compass is made of two branches, with two points each. Several types exist: - 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 determins the enlargement factor
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. 3 : Technical drawing|Drawing aids|Stonemasonry tools |