There are two eccentric dials on the upper surface. The outer, silvered one, 0 to 30, numbered by 5 and divided to 1. The inner 1 to 12, numbered by 1 and divided to 1/2. An index is fixed to the centre of these dials. A pierced and engraved detachable disc with a small index can be fixed to the central index by means of a hook. The index on the disc advances through one division of the silver dial each time a plunger (now missing) is operated. The index in the centre of the dials is geared down 48:1 from the rotating disc and rotated through one quarter of a division for each rotation of the disc. The surface is decorated with strapwork and scrollwork. An inscription in a oval cartouche reads 'CVM GRA: ET PRIVI:S CAESAR: MAI:', an indication that the instrument was manufactured for the Holy Roman Emperor.

The dials are set into a drum on the same arbor as the disc, within the body of the instrument, onto which the paper strip is wound, one end of which is fixed to the disc. The tape is advanced 4 mm for each operation of the plunger. The tape is unwound from a spool running freely on its arbor and passes over the compass box (now empty) on the side of the instrument. Three spikes project upwards from the compass needle and, when the plunger is operated, the whole compass box is lifted up and the spikes make indentations on the tape, giving a record of the compass bearing of the instrument at that instant.

The instrument was formerly in the Bernal collection and was purchased for the Museum in 1855. It is described in H. von Bertele, "Early Clocks in Denmark", Horological Journal 96 (1954), pp. 789-91; 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. 92 ff., no. 269.