Diptych dial for latitude 51° North. This dial has two leaves that fold flat when not in use. Leaf Ia contains an equinoctial dial with a projection of solar declination lines. Leaf Ib carries the Southern half of the equinoctial dial and the vertical dial for use with the string gnomon. Leaf IIa displays the compass, surrounded by an hour scale. At the bottom of the leaf is a semicircular brass attachment for the string gnomon that extends over the compass. Printed on the compass card is a degree circle and a wind-ring. There are two further scales (possibly some form of table) and an eight-pointed star at the centre. Leaf IIb is blank. On the right side of the dial is a brass strut with a latitude scale for use with the equinoctial dial. On the compass card, the dial is signed 'Henricus Sutton Londini fecit. 1661'.

This is one of very few diptych dials to have been made in England, and its style is quite different from both the French and the German diptychs. The equinoctial dial on the upper leaf also incorporates a polar dial, and there are both vertical and horizontal dials inside. The relevance of the table in the compass is unclear. A slightly more elaborate version of this instrument (with a Gunter quadrant added to the outside of the lower leaf) is in a private collection in Belgium.

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