Cylindric compass box is deepened into the center of square plate. Scale on the surface of plate consists of 100 devisions (twice 0-50) with numbering in 5. In the corners of the square are 4 men's portraits with notes: АRСНIMEDES (Archimedes) with globe, АРOLLONIVS (Apollonius) with cone, EVCLIDES (Euclid) with ball and caliper and DISCIPVLVS (Pupil) with open book.