Small circumferentor with fixed and moveable sights, 1571-1600.
© Science Museum / Science & Society Picture Library
The scale on this circumferentor is engraved on the circle '10(10)360' clockwise, by degrees. Circumferentors (with a full 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.