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 edges are scales corresponding to different map scales - 1:63,360, 1:250,000 and 1:80,000). Attached to the centre is a thread, which is used to lay off bearings. The protractor has a hand-made paper case with 'H.T.A. Bosanquet' and 'C.O. Portractor' written on it in ink.

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).