One side of this quadrant carries a degree scale, an horary quadrant set for latitude 42° (Rome) with hour lines for Italian hours, and a magic square at the apex.

On the other side are a windrose (inside of which is a magnetic compass complete with a magnetic needle) and a scaphe dial with cover. A relief mask is placed at the apex.

Stored in a red leather case with matching velvet lining.

The quadrant belonged to Gregory XIII and is signed by Giovanni Battista Giusti ("Ioannes Batis"). It is listed in the inventory of the "effects" of Grand Duke Ferdinand I de' Medici.