Astrolabe with a single tympanum for latitude 43°40' (Florence). It is placed on an octagonal table, whose inclination is adjustable. There are a rete and an alidade. The planisphere is surrounded by: the calendar with the names of the months; a shadow square engraved on an arc in an eccentric position; a zodiac circle; a Tychonic scale for dividing the degrees into twelve parts; a windrose; and a degree scale.

Originally attributed to Egnazio Danti, it is now regarded by G. L'E Turner—on account of the punch-marks and the engraving characteristics—to have been made in the Florentine workshop that produced the instruments signed by Giovanni Battista Giusti.

The instrument was preserved in the Uffizi Gallery, and Galileo himself used it for astronomical calculations. For this reason it is known as "Galileo's astrolabe."