Diameter: 250 mm Functions: Protractor chartAngle : Divisions at 1° and 30' intervals at 178mm/7" diameter increasing to 381mm/15' intervals at 279mm/11" diameter.Features : Dedicated chart especially designed for checking angles with exceptional clarity. Suitable for use at any magnification. Grid divisions: 10X : 0,1 mm 20X : 0,05 mm 50X : 0,02 mm100X : 0,01 mm Description: Line width: 0,05, 0,08, 0,1 and 0,12 mmGraduation lines, linear: Error limits: (0,04 + L/3000) mmGraduation lines, angular: Error limits: 25 angular secondsThermal extension coefficient of plastics: 2,7 x 10-5 K-1