Diptych dial for latitude 45° North. Rectangular boxwood dial in book format, consisting of two leaves that fold together when not in use. Leaf Ia carries an equinoctial dial that is combined with dials for Italian hours and Babylonian hours. Solar declination circles are marked for the beginning of each summer zodiac sign and labelled with zodiac symbols. The pin gnomon is missing.

Leaf Ib forms the southern part of the equinoctial dial and is also combined with dials for Italian hours and Babylonian hours. Solar declination circles are marked for the beginning of each winter zodiac sign and labelled with zodiac symbols. A groove on the right-hand side presumably held a strut for setting the latitude. Leaf IIa has a horizontal dial combined with a compass for use with a string gnomon that is attached between the inner surfaces of the leaves. The compass is on painted card. Leaf IIb is bare apart from a brass circle arc (broken at 50°), set in a groove. This arc is divided 5°-90° and is for use with the equinoctial dial. There are brass hook fasteners on the sides of the dial.
This unusual diptych dial is probably Italian, judging by the inclusion of Italian and Babylonian hours on the equinoctial dial. The latitude of 45° North corresponds with Northern Italian cities, such as Milan and Venice. The equinoctial dial is set using the brass circle arc, which is stored on the back of the dial.

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