Circular fiberite discs concentrically mounted, one with circular slot with increasing width, the other with fixed slot. Discs preset for heights of common objects (given in table on back). Small viewing aperture, attached to knotted cord, running through hole in centre of discs, and weighted at other end. Held close to the eye and discs moves away until object just fits the aperture. Distance measured by length of knotted string in 100 yard units. Three sets. Clement Clarke Limited. Kingston Patent.