Diptych dial for latitudes 42°-54° North. Rectangular ivory dial consisting of two leaves that fold flat when not in use. Leaf Ia is a standard windrose (see related terms), except eight winds are named in Italian and the cardinal points are named in Latin and German. Leaf Ib is as standard. Hours are numbered downwards on the left-hand side (daylight hours) and upwards on the right hand side (night hours). Below the dial is a table of latitudes, mainly for German towns. There is no vertical dial.

Leaf IIa is as standard except there are three concentric hour scales on the horizontal dial marked 54°, 48° and 42° respectively, for use with the different positions of the string gnomon. Thomas Ducher's makers mark of a crowned snake appears twice in the compass. There are two scaphe dials for Italian hours (none for Babylonian). Leaf IIb features a standard lunar volvelle surrounded by circular epact tables marked for Julian and Gregorian epacts. These tables have been labelled incorrectly (i.e. Julian as Gregorian and vice versa). This error is typical of the work of both Ducher and his son, Joseph. Their tables also always began with the same numbers - 7/17 regardless of the year in which the dial was made.

The dial is very similar in style to that by Joseph Ducher in the Harvard collection (Lloyd (1992), p. 56, no. 9).

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