RARE Vintage Russian proportional divider compass ЦП-1 "TzP-1" in original plastic scale-case. 
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. 
The reduction compass is made of two branches, with two point 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.