This very simple example of a universal equinoctial dial is in the form of a compass box (now empty), with lid and hour ring fixed to the same hinge. In the compass box are engraved in unusual (pseudo-Chinese) writing, letters for the initials of the cardinal points 'S', 'O', 'M', 'O'.
The hour ring is numbered from IIII to XII and from I to VIII and has a pivoted cross-piece to which is fixed the gnomon. In use, this is plugged into a small hole projecting into the compass box from a ring, held at the right height by another perpendicular brass band.
The top of the lid is a primitive form of nocturnal, divided into 12 parts, each subdivided in two, with further divisions into six. Each part is engraved with a letter, which is possibly the initial of the names of the months in Italian or Latin. A double ended alidade is pivoted at the centre of the lid.
The surfaces of the whole instrument are badly distressed. The instrument was found in the bed of the river Crane at Isleworth. It was presented to the Museum by H. C. Pidgeon in 1853, and it is described in F. A. B. Ward, A Catalogue of European Scientific Instruments in the Department of Medieval and Later Antiquities of the British Museum (London, 1981), p. 46, no.119.