The outer side of the upper leaf of this brass diptych dial is decorated with strapwork in the lower part, and with two coats-of-arms between columns and arches. On top of both is the date 1566, engraved twice. The compass viewing hole is heart-shaped.
The inner part of the upper leaf has a vertical string gnomon dial indicating common hours from 6 to 12 to 6. A spade shaped aperture was filled in with a brass plate of the same shape at about the centre of the dial.
The inner part of the lower leaf has a compass (ring, needle and glass are detached) with the cardinal points abbreviated '[three dots] SE [three dots]', 'ORT:', '[three dots] ME [three dots]', ':OCC:' and a line for magnetic deviation. The horizontal string gnomon dial (string missing) indicates common hours from IIII to XII to VIII, divided to half hours with lines and to quarter hours with dots. The hour lines radiate from a sun effigy. At the centre of the figure is the signature and date ' ?C ? S ? 1566'. On the left side is a brass hook and ring latch for keeping the dial open when in use.
The outer side of the lower leaf is engraved with a blank rectangle with four lines to the corners, and three bun feet. A clasp keeps the dial closed when not in use.
The instrument was formerly in the Bernal collection (no. 3959) and was purchased in 1855. 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. 43, no.103.