Disk with folding index arm rotating on a square plate carrying fixed sights for altitudes. The diurnal hours and night hours are marked for several latitudes. There are also markings for the climates. On the back are a nocturnal and sundial, a 90° quadrant with a shadow square, and the sine scale. Made by Georg Zorn, about whom we have no information. Brought to Florence from Germany by Prince Mattias de' Medici in the first half of the seventeenth century.