Diptych dial for 40°-50° North. Rectangular ebony dial consisting of two leaves that fold together when not in use. The outer surfaces of the leaves are blank. Leaf Ib carries an indented circle containing a table of latitudes on printed paper, which is stuck to the leaf and decorated with gold swirls. The centre of the top half of the table carries a latitude scale numbered (rather crudely) 40, 42, 44, 46, 48 and 50. Beside this is a metal rod along which runs a slider; the string gnomon (attached between the two leaves) passes through this slider. By moving the slider, the latitude angle of the string can be adjusted.

Leaf IIa features an ivory horizontal dial with scales for various latitudes and hour-lines radiating from a central circle. Below is a compass, offset 8° East of North to allow for magnetic variation. It has a painted compass card with eight points named in French, and North is further indicated by gold fleur-de-lys. The blued needle is bent, surmounted by brass pyramidal pivot and covered by a mica plate. The leaves are held together by two metal hook fasteners and metal hinges.

The sliding scale for the string gnomon on this dial makes it useable for all latitudes between 40° and 50° North, rather than a selection, as occurs on the Nuremberg diptychs. The table of latitudes consists largely of regions rather than towns, which provides a rough guide for all the areas of France and some beyond its borders.

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