A Vickers machine gun clinometer sight Mark III, marked Marked No. 53
Note the adjustment for depression and elevation as well as the spirit level.
Manufactured in 1918 by Troughton & Simms, such sights were used to find the angle of elevation on sustained-fire water-cooled machine guns popular from the Boer War through the 1960s.
Vickers machine gun emplacement in a sangar, North West Frontier Province between the wars. The pouches on the back on the No. 2 (with his hand up) are for clinometer and the foresight bar deflector – seldom seen in the field. The headdress of British Indian troops was normally the khaki puggaree which varied by the soldier’s religion–Muslims with a pointed kullah skullcap inside the puggaree and Sikhs with a more open version that allowed their uncut hair to remain in a bun atop their head, while most Hindu troops wore a simple turban. Photo via British Empire Uniforms 1939-45.
The concept was used by all sides with such guns. Below is a 1914-ish German Spandau crew in a defilade position ready to hose down attackers from comparative safety, via clinometer.