'Harper Overhead Height Check'. Device used to identify allied and axis aircraft flying overhead. Approximately 15cm long x 12cm diamter in the form of an octagonal wooden tube. Designed to be held 18 inches from the eye by means of a cord stowed within the end tube and attached to a wooden stopper. The wingspan and aircraft type can then be read off the sides of the device. Aircraft noted on the sides include the Stirling, Halifax, Fortress, Ju52, Sunderland, Liberator, Ju88, Spitfire, Defiant, Mustang, Swordfish, Ju87, Battle and so on. These were available for private purchase by keen aircraft spotters, ATC, Home Guard, ARP and so on. Advertised in the 'Aeromodeller' magazine of June 1943 which states that over 7000 were in use. Some wear and staining to the markings through use/storage. The stopper and cotton are easily removed for use. Extremely rare to find. Stock code M17532.