This instrument is a combination of a prismatic compass and an inclinometer. It was patented in 1909 by f J.C. Asten, Optician, and Francis Barker & Son Ltd. It was used by the artillery.
This instrument could be utilized together with different gun types, among others the French 155mm howitzer type M1918.
Text engraved on the front is: "Angle of sight instrument J.H.Steward Ltd 1916" , also a broad arrow and the # 102