The instrument consists of two disks connected by an arm. On one side of the larger disk is engraved a nocturnal (incomplete); on the other side is a quadrant, set for latitude 43°44' (Florence), with hour lines for Italian hours and a shadow square. The surface of the smaller disk is engraved with many astronomical scales. Made by Eufrosino della Volpaia. Provenance: Vincenzo Viviani bequest.