This binocular was used during WW I. On the front you see the "Broad arrow", which means that this binocular was purchased by the British Army.
In one circle you find "R sch 10/40" In the other "AM". The Air Ministry was formerly a department of the British government with the responsibility of managing the affairs of the Royal Flying Corps (R.F.C.) which existed from 1912 to1918. April 1918 the Royal Air Force (R.A.F.) was founded. The Air Ministry existed from 1.4.1914 to 1964.