He is probably best known as designer of the surveying instrument known as the graphometer. The dioptra was replaced as a surveying instrument by the Theodolite. The groma or gruma was a Roman surveying instrument. Transit Road, surveyed by Joseph Ellicott, was named for an important surveying instrument. Ltd. (currently Topcon Sales corporation), a surveying instrument sales company. The graphometer, semicircle or semicircumferentor is a surveying instrument used for angle measurements.