© Science Museum / Science & Society Picture Library
This instrument is inscribed with the scale, punched on the circle, '0(5)90(5)0(5)90(5)0', by degrees. It has one pair of fixed sights only and the compas is mising. Circumferentors (with a complete circle scale) and graphometers (with a half circle scale) were widely used through the 17th and 18th centuries for angle measurement. A joint on the support allowed for both vertical and horizontal use.