This instrument consists of a plotter mounted on a roller. The plotter contains distance scales at 1:20,000, 1:40,000, and 1:80,000 to fit the N.O.S. Coast and Harbor Charts, as well as an inch scale. Included are a semi-circular protractor for measuring courses and bearings against a meridian on the chart, and two quarter circle protractors for measuring courses and bearings against a parallel of latitude. Courses and parallel lines are transferred and kept parallel by means of two rollers which are mounted on a slide axis. Used for measuring or laying off courses and distances on a nautical chart. Instructions included. Dims: 3.5″ x 12.5″.