Silver, parcel gilt, engraved with inscriptions, numbers and lines
height 4.6 cm, diameter 6.1 cm
Within the quadrant, with a gilded scale of twice 90°, is a shadow square, also gilt. The tips of the two rules, gilt side to the front, silver on the back, which are mounted at the center of the diameter, terminate flush with the edge of the quadrant. Shadow squares were originally a feature of the back of astrolabes, but since the Middle Ages had been used independently, and as such were very common in the C16. They were used for measuring angles and distances, or for telling the time. However, on this instrument the lines necessary for the former are lacking; its small size and precious material indicate rather that it was used simply for telling the hours of the day.