A rare WW1 British military range finder, dating from c.1915. Designed by Charles Hymans of Cambridge, it was patented in 1915 (Patent No. 4493/15). The instrument has a brass body with an oxidised finish containing the rangefinder elements, a prism and a sliding lens with integral scale. Patent number, 4493/15. On either side of the body are measurement tables to be used in conjunction with the scale on the sliding lens frame. Comes with a brown leather case with no markings on it . The instrument has some dirt inside and on the pullout frame , prism looks good , glass on the pullout frame is not damaged . I have no idea how to operate this instrument, no quarantee on a correct working .Dimensions: 75x 32x20 mm.Found a few pages of the manual on the internet, and how to use it . Please see all pictures as they are part of the description.