This is a 4 x 15 inch transparent protractor plotter which is very popular with boaters, and the U.S. Power Squadrons. It is printed in two colors, and laminated for protection. The orientation of the protractor makes it particularly easy for plotting celestial lines of position. The edges are calibrated in both statute and nautical miles for chart scales of 1:40,000, and 1:80,000. (C-Thru model P-72, List $6.50)