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. Along the top and bottom edges are scales in metres and yards (corresponding to scales commonly used on continental maps at the time - 1:100,000 and 1:80,000). Attached to the centre is a thread, which is used to lay off bearings. The maker's name is inscribed across the centre of the protractor, with the initials 'H.T.A.B.' roughly inscribed near one corner.

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).