By B.B. Co. Approximately 33 x 9.5cm. Transparent acetate ruler / plotter graded for satute miles at scales 1 : 1000, 000 and 1 : 500, 000 for use in plotting routes on flight maps. Formed part of the navigator's kit and is US Army Air Force marked. Slight curvature of the acetate but otherwise in very good condition. A rarity. Stock code M22289.