Diptych dial for latitude 49° North. This is a miniature diptych dial consisting of two leaves that fold flat when not in use. Leaf I is made of ivory and leaf II has a wooden core sandwiched between the ivory. Leaf Ia features a lunar volvelle. Leaf Ib contains the vertical dial with hour-lines radiating from a double semicircle. Leaf IIa displays a compass with the hours for the horizontal dial set around it. The hour-lines radiate from the string gnomon. This is for latitude 50° and is attached between the inner surfaces of the two leaves. The compass has the cardinal points marked in Latin and is offset 20° West of North to allow for magnetic variation.

There are two maker's marks in the compass bowl: a fleur-de-lys on the right-hand side and a 'B' on the left-hand side. There are also three red decorative motifs. A brass pin for keeping the leaves aligned when closed is on the bottom right-hand side. Leaf IIb is bare. The leaves have a copper hook fastener and a copper hook to hold the dial open.

Even though this instrument is unsigned, there are two clues as to whom the maker might be. The fleur-de-lys that appears in the compass bowl might suggest Lienhart Miller as a maker, but the 'B', which is also set in the compass, indicates possibly the Karner workshop. The style of the dial is closer to instruments originating from that workshop during the 18th century.

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