Alvin - Beam Compass - Ungraduated - The Alvin Beam Compass includes two 13 inch ungraduated beam bars and one coupling to accommodate circles up to 48 inch diameter. Springloaded thumbwheel on the top of each slide assembly allows for smooth and precise adjustments. Comes complete with interchangeable ruling pen, pencil, and divider legs. Includes spare leads and needlepoint. Alvin is one of the primary sources for drafting supplies and drawing equipment in the country. Creative Coldsnow is a pround retailer of Alvin graphic arts, drafting and fine arts products.