Cellulose-based plastic plotting instrument for air navigation. The protractor is square with a central circular degree scale marked from 0 to 360 in degrees. At the centre is a hole, to which a thread should be attached to lay off bearings. The thread is now separate. The maker's name is inscribed with the degree scale, with the initials 'H.T.A.B.' roughly inscribed below.

This is one of a number of items formerly belonging to Henry Theodore Augustus Bosanquet (1870-1959), who was a leading figure in the development of air navigation in Britain during the First World War. The Creagh-Osborne protractor was one of the instruments Bosanquet recommended for air navigation in the 'Royal Naval Air Service Kite Balloon Training Manual' (1917), although this version is simpler than the one described in the manual. ZBA4461 is an example of the more complete version.