Used by navigators for over 50 years. This is a 15” course plotter with a semi-circular protractor scaled from 180 degrees to 360 degrees inside. Lower edge scales 1:80,000 and 1:40,000 to accommodate N.O.S. charts. For north and south courses, a small auxiliary protractor scale is printed inside the larger one and is used against a parallel of latitude. The upper edge is scaled 1-inch equal to 20 miles to accommodate the VPOS Universal Plotting Sheets.