Ruler consisting of a brass plate engraved with different scales of proportion. On the front is an arithmetical scale divided into 60 equal parts, a geometrical scale divided into 200 decreasing parts, and a polygon scale. The back is engraved with a scale of chords, a scale of metals, a polyhedral scale, and a caliber scale for iron balls The instrument is probably related to the surveying instrument inv. 680, also made in Urbino. The front carries the Medici coat of arms.