The Latin inscription—"INSTRVMENTVM PER CIPIENDI DISTANTIAM PER SVPERFICIEM"—indicates that the instrument is used "to find the distance by means of the surface." It consists of a 125° circular sector with a 90-mm radius. At the center is a fixed ruler divided into 44 parts and a mobile radius. A second ruler, also divided into 44 parts, is hinged to the end of the mobile radius. Each ruler is equipped with two sights. On the back of the instrument are three small brass tubes, perhaps to fasten the instrument to a support. The distance was measured presumably from two surveying stations whose distance was proportional to the length of the mobile arm; the lines formed a triangle with one side in a known proportion to the unknown distance. The construction characteristics and elaborate engravings suggest an attribution to Baldassarre Lanci. Provenance: Medici collections.