This instrument is identical to item inv. 3167 and, like it, is attributed to Christoph Schissler. It is also called Jacob's staff, a reference to its presumed inventor, Jacob ben Machir. The original model consisted of a perpendicular vane sliding on a longer rod. In this version, the vane is fastened to the end of the longer rod. The latter has a hollow section containing a thinner rod that can be pulled out as an extension. The vane and rod, perpendicular to each other, respectively represent the base and height of a triangle whose sides are the observer's lines of sight. The instrument applies the properties of similar triangles to the measurement of terrestrial and celestial distances. Brought to Florence from Germany by Prince Mattias de' Medici in the first half of the seventeenth century.