Diptych dial. This dial consists of two ivory leaves that fold flat when not in use, supported by four large ivory feet. The surfaces are divided into four leaves. Leaf Ia features a lunar volvelle with a rotatable disc made of brass, numbered in Chinese and marked with Chinese characters. It has a long brass index arm with a pointer at one end (used for finding the time, by rotating the arm until the shadow fell on the inside of the ring). Leaf Ib is adorned with circular geometric decoration. Also, a slot in the left hand side holds a brass strut for setting the latitude. The horizontal dial, numbered in Chinese, is on leaf IIa.

A simple compass, with no markings, is set in the middle. Along the left-hand side is a latitude scale and holes, into which the pin of the strut can be set. The gnomon is missing. Leaf IIb features a nocturnal consisting of a volvelle marked with 24 seasons, all in Chinese. A small brass index arm is pivoted at the centre. Four Chinese characters indicate two circumpolar stars, which can be used for finding directions.

This Chinese dial clearly shows the influence of the Jesuits and reflects the Western forms and functions. It may be connected to Adam Schall von Bell, a German Jesuit who worked in China during the 17th century, and who is known to have made portable ivory sundials. A similar dial signed by Schall von Bell and dated 1639 is now at Stonyhurst College, Lancashire.

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