Alvin 117PM series metric drafting scale 12" has graduations 1:20, 1:33 1/3, 1:40, 1:50, 1:80, 1:100 with one edge calibrated to the millimeter. The most popular Alvin scaled ruler is made from satin-finished impact plastic with tapered edges and black easy-to-read printed graduations that won't rub off.