The outer face of the cover represents astronomy as Urania holding a globe and overlooked by sun, moon and stars. The engraved image is surrounded by a hatched border.

The inner face of the cover carries a horizontal dial for about latitude 48? with a folding gnomon sprung to the vertical. The dial serves either as a direct-reading lunar dial or as a solar dial. The hours run from 4 to 12 to 8 on a silvered disc with a circular aperture to graphically set the age of the moon. The disc can also be set against a fixed scale of the age of the moon from 1 to 29[1/2]. The decorated corners of the face seem to represent the winds.

The main box contains the compass and an inclining dial. The compass is 25 mm in diameter and is simply marked for variation. The dial has a folding gnomon and the hour scale runs from 4 to 12 to 8. The dial plate can be inclined for latitudes from 42? to 62? at 2? intervals.

The base of the instrument carries the signature 'Ioannes Gruber Norimb:' and a table for the latitudes of 24 places.

Provenance: Michel Collection; Billmeir Collection (57-84/52)