The obverse of the plate has two circular scales along the edge as follows (from the outside: a) A zodiacal scale with the usual Latin names of the signs in Latin (some abbreviated, 'Chapri' for Capricorn), each sign with a 30 degree scale, numbered by 5 and divided to 1; b) A calendrical scale with the usual Latin names of the months (some abbreviated) and the corresponding number of days, numbered by 5 and divided to 1. The equinoxes are at the 10th March and 131/2 September.
The centre of the disc has markings for a plate for the sixth climate, marked 'C 6'. The almucantars are marked for every 5 degrees, numbered by 5 from 5 to 75. There are hour lines for equal hours 1 to 24. The horizon is marked 'ORIZON', and east and west are marked 'ASCENDENS' and 'DESENDENS'.
The obverse has a double degree scale, clockwise 0 to 360 and anticlockwise 90 to 0 to 90 to 0 to 90.
The top half of the disc is marked as a double horary quadrant, each numbered 1 to 6 to 12. The lower half is engraved with a double shadow scale to the base 12, numbered by 1. The date and the signature '1507 OPVS FALCONI' are given in the centre of the scale.
The rete is damaged and part of the tropic of Capricorn is missing. The ecliptic is marked with the first letters of the zodiacal signs, each sign has a 30 degree scale, numbered by 10 and divided to 5 and 1. The star pointers are wedge shaped.
The instrument was purchased in 1894 and 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. 114, no. 330.