Cannon dial for latitude 50° North. The cannon sits on a circular marble base on which is an hour-circle and a triangular iron gnomon. The compass is set into the base beneath the gnomon. On the printed compass card there is a 16-point rose with the points named by English initials. The cannon has a 200mm barrel and is mounted on the meridian line between two supports, which can be adjusted by a screw to alter the elevation of the cannon. Parallel to the cannon and to either side of it are two vertical armillary quadrants with adjustable radial arms. The burning glass is missing.

This cannon dial is considerably less ornate than AST0179, its French counterpart in the NMM collection. Cannon dials (or 'time guns' as they were occasionally known) were popular in the 18th century. A burning glass mounted above the plate would receive the sun's rays at noon, so providing the heat to light the fuse at the end of the miniature cannon, causing it to fire and thus provide a signal for midday.

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