The instrument, possibly made by James Kynvyn in 1595, is now incomplete. Of the horizontal circle with the degree scale only one half (from 180° to 360°) remains. However, it does still carry the base for the azimuth compass (missing). A quadrant with a nonius is fitted at right angles to the base. At right angles to this second plate pivoted a diopter (missing) for measuring heights, while the compass served to determine position angles. The instrument was thus used to calculate the coordinates of celestial bodies (altitude above the horizon and position relative to the magnetic meridian). Provenance: Robert Dudley bequest to the Medici collections.