Douglas Combined Protractor and Parallel Rule

The W & G Douglas combined protractor and parallel rule is a square panel of translucent plastic with a ground surface for plotting chart lines. It consists of a centimetre ruler and angle bearing markings around the perimeter, a central compass, with four points and a 0:20 cm marking, set out on an 8 x 8 square grid. The protractor is housed in a double sided, green, printed square card sleeve. The front of the sleeve features a description of the product and a series of warnings on usage, while the back displays instructions and examples of the various uses of the parallel rule including laying off a course bearing, finding departure or latitude, find a magnetic course or bearing from true, fixing positions by angles and plotting lines of position.