Royal Artillery Barr & Stroud patt Field Rangefinder 1918 silver badge

A rare and very unusual fine quality First World War period 'Field Rangefinder pin badge' the reverse impressed with Birmingham silver hallmarks for 1918 and maker's details 'S.B&S.Ld' (S.Blanckensee & Sons Ltd, Birmingham.). Very good condition, retaining original pin fittings. Length 52mm. The company of 'Barr & Stroud' was founded in Glasgow, Scotland in 1888. They developed this pattern of rangefinder just prior to the Great War.