Italian circumferentor ('ipodimeter') with eccentric alidade, 17th century.
© Science Museum / Science & Society Picture Library
The inner scale on the circle of this circumferentor is engraved; 'Aqvilo solanvs evrvs avster africvs favonivs chavrvs septent'. 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. The sights on this instrument are set off to one side.