The instrument is in the form of square-section box with a lid. The lid is hinged in such a way that, when opened, it lies on the same surface as the rest of the instrument.
The outer face of the cover leaf is decorated with a central crested coat of arms surrounded by the name 'IOAN BAPTISTA NAVMAN' in a scroll. In each of the four corners is engraved an emblematic or mythological image.
The inside face of the lid carries a horizontal dial with the hours running from 4 to 12 to 8, and with the hours from 5 to 12 to 7 divided to 1/2 and 1/4. The silver folding gnomon is said to be a replacement and sits above an engraving figure of the crescent moon.
The main box contains a compass of 29 mm diameter whose glass is held in place by a ropework ring-spring. The cardinal points are labelled 'SE', 'OR', 'ME' and 'OC'. Around the compass is circular scale of equal parts 1 to 12, divided to 1, 1/2, 1/4 and eighths. The scale and compass can be rotated together. The corners of the face are stipple-engraved.
The underside of the instrument is blank but the sides carry the inscriptions: 'NICHTER KEIT IST EIN LERIN ALER GVENTEN KVNST' and 'DIE. VER . GVNGERVNG DERMAS . STAB . VND . AVF STEIGVNG . SCHREG . AB . ZV . NEMEN'.
Provenance: Michel Collection, Billmeir Collection (57-84/54).