Folding rule consisting of two wide, flat legs engraved with: the degree scale, the shadow square, the windrose, a scale of equal parts, and a list of forty-two European cities with their respective latitudes. Resembles item inv. 2514 except for the following points: different material (non-gilt brass); magnetic compass, now missing the glass cover and magnetic needle; different hour markings; lack of motto on brevity of life; full signature of maker, Antonio Bianchini. It appears in the Trattato di diversi istrumenti matematici (a manuscript dated to 1593) by Antonio Santucci under the name of "Gran Regola di Tolomeo" [Great rule of Ptolemy]. The instrument was used to measure terrestrial and astronomical distances with the help of a ruler (now missing) hinged to one of the legs. The ruler served as the base of the many triangles formed by folding the instrument. The base represented a measure proportional to the distance to be calculated. Provenance: Medici collections.