Rectangular 6 in scale / protractor in ivorine with UK military broad arrow insignia.
Some of these scale / protractors were made with a metal core and this could affect compass bearings. This example has no metal core. The scales on one side, from top to bottom are: yards 1 inch = 1 mile; yards ¼ inch = 1 mile; miles ¼ inch = 1 mile; miles ¼ inch = 1 mile; yards 1:20,000; metres ¼ inch = 1 mile; metres 1 inch = 1 mile. On the other side below the protractor scales are: metres 1:80,000; metres 1:25,000; miles 1:250,000; yards 1:250,000; yards 1:50,000; yards 1:25,000.