This perpetual wheel, made by Antonio Santucci, is dedicated to Christine of Lorraine, wife of Ferdinand I de' Medici—as evidenced by the Medici-Lorraine coat of arms. There is no precise date, but, as the dedication indicates, the engraving was made after the calendar reform promulgated by Pope Gregory XIII in 1582.
The engraving comprises five concentric wheels for finding sunrise, the phases of the Moon, mobile feasts, the Dominical letter, the golden number, and the epact at any given time of year. An armillary sphere is depicted at the center. Over the wheel, two male figures with compasses are measuring stellar and physical distances on a celestial globe and a terrestrial globe.