The front of the quadrant is marked with lines for unequal hours, superimposed with a shadow square to the base 12, numbered by 4 and divided to 1. Along the curved edge is an altitude scale 0 to 90, numbered by 10 and divided to 5 and to 1.
The scale of months and corresponding zodiacal signs slides along the altitude scale in a groove. It is marked with the usual Latin names of the months and the Latin names of the signs, all abbreviated. Each month is has the corresponding number of days (February apparently with 30 days), divided to 10 and 2. Each sign has 30?, divided to 10? and 2?. The equinoxes are at 12 March and 15 September.
The plumb bob appears to be a later replacement.
The reverse has two circular scales (from the outside):
1) The usual Latin names of the zodiac (some abbreviated), divided to 10? and 2?.
2) An eccentric scale with the usual Latin names of the months (abbreviated) with the corresponding number of days, divided to 10 and 2. The equinoxes are at 12 March and 18 September.
A central disc has been engraved at a later date with a shadow scale to the base numbered 1 to 1, divided to 1/3. Over this disc rotates an alidade with two sighting vanes and engraved at a later date 'LINEA FIDUTIA'.
The instrument was purchased in 1972 and is described and illustrated 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. 55 (with plate XX).