A graphometer consists of a graduated semicircle with a pair of sight vanes at either end, and a movable alidade with another pair of sights at either end. The form was introduced in Philippe Danfrie, Déclaration de l’usage du graphomètre (Paris, 1597)
The tool is fine and complete, but the fine wire crosshairs need to be replaced. Beautifully engraved. 7 3/4 x 4 1/4 inch box is covered on embossed leather and missing one latch. What a find!