This astrolabe has three tympanums, two of which are made for latitudes 41° and 43° (Naples, Pisa) and 45° and 48° (Piacenza, Bavaria, and Vienna) respectively. The third tympanum carries: (1) on the front, a geographic planisphere, with equator, the tropics, and the names of the continents; (2) on the back, a degree scale, a zodiacal circle, a calendar, a diagram for converting equal hours into unequal hours, and a shadow square. A small magnetic compass is lodged in the throne, on which the year of construction is indicated. The back has a celestial planisphere with the orthographic projection of Juan de Rojas. The rule with an orthographic projection of the meridians lacks a cursor. Provenance: Vincenzo Viviani bequest.