Patent US 4,428,668

An optical range indicating device, having no moving parts, having a pair of mirrors arranged to embody the principle of triangulation, one of the mirrors being positioned to sight the object to be viewed and having thereon distance indicating indicia, the other mirror being positioned to provide a view of the image of the sighted object and of the distance indicating indicia the mirrors being unitarily pivoted about an axis to align a direct line of sight view of the sighted object with the reflected image of the sighted object superposed upon the reflected image of the distance indicating indicia as seen on the other mirror to indicate the distance to the sighted object.