グラフォメーター

Also known as semicircle, semicircumferentor

thumb|Butterfield compass graphometer thumb|A German graphometer in Göttingen, Stadtmuseum. The instrument is on its side. At the back, the socket for a Jacob's staff can be seen. The graphometer, semicircle or semicircumferentor is a surveying instrument used for angle measurements. It consists of a semicircular limb divided into 180 degrees and sometimes subdivided into minutes. The limb is subtended by the diameter with two sights at its ends. In the middle of the diameter a "box and needle" (compass) is fixed. On the same middle the alidade with two other sights is fitted. The device is mo