Forged astronomical compendium with no measurable latitude. On the outside of the lid is an engraving of mathematicians using various kinds of instruments. Inside the lid is an astrolabe plate. Pivoted at its centre is a silver lunar volvelle, with long pointers on both discs, and a brass armillary date ring (rete), which has cross struts that also support a brass ecliptic ring. The lower disc of the volvelle has a lunar-age circle and the upper disc contains an aspectarium; a circular aperture revealing a pictorial display of the phases of the moon. Inside the base is a horizontal dial, with a brass gnomon, and a compass set at the centre. The compass has cardinal points marked in Latin and is incorrectly oriented.

This instrument comes into the category of forgery, since it was clearly made with intent to deceive. The object is unlike any of the authentic Schissler compendia. Moreover, the inscription declares the instrument to have been made in Prague, whereas Schissler spent his whole life in Augsburg. Another obvious fault with the inscription is that it has been engraved rather than stamped. (Schissler exclusively used a punch and stamped both his letters and numbers.) The engraving on the lid of the compendium is a good copy of the title page of Peter Apian's 'Instrument Buch' (1533). The dial on the inside of the instrument has been incorrectly engraved. For example, the hour-lines do not correspond to any latitude. There are similar components in a diptych dial at the Adler Planetarium, Chicago, and in another diptych dial in the Beltrame Collection in Vicenza.

For more information regarding this dial please refer to the OUP & NMM catalogue, 'Sundials at Greenwich'.