The mater is graduated 90? to 0?, 0? to 90?, 90? to 0?, 0? to 90? clockwise, numbered by 5? and subdivided to single degrees. The rim is rivetted to the back plate. The inside of the mater is marked with circles for the tropics and the equator and the east-west and meridian lines.
The throne, which is rivetted to the rim, has the characteristic Hartmann shape: two roses, a rosette, and two fir cones in a triangular layout supported by foliate scrolls.
The rete is in the usual Hartmann shape which consists mainly of arcs of circles and split ends of the circle for the tropic of Capricorn. It has 27 pierced star pointers, some of which are bent or broken. The following stars are named: 'CAVDA CETI', 'VMB ANDRO', 'VENTER CETI', 'GORGON', 'NARES CETI', 'CAPRA', 'OCVLVS TAVRI', 'PES SIN ORONIS', 'CANIS', 'PROCION', 'HIDRA', 'REGVLVS', 'CRATER', 'CAVDA LEON', 'CORVVS', 'SPICA [Virgo]', 'CAV VRSE', 'ARCTVRVS', 'CORONA', 'MAN<VS> SERP', 'CAP SERP', 'LIRA', 'AQVILA', 'DELPHIN', 'HOLOR', 'HVM EQUI', 'CRVS PEGASI'.
The ecliptic is marked with the usual Latin names of the zodiacal signs and is divided into 12 ? 30?, numbered by 10?, divided to 5? and subdivided to single degrees indicated by serrations on the outer edge. The equinoctial bar is counterchanged six times: on both sides of the ecliptic, between the ecliptic and the tropic of Capricorn and between the ecliptic and the central disc. The reverse of the rete is marked with an 'F' at the intersection of the tropic of Capricorn and the solstitial bar. This letter is also to be found on the three plates, on the reverse of the alidade and on the bottom edge of the mater.
The three plates are marked on both sides with circles for the tropics and the equator, azimuths for every ten degrees, numbered by 10?, and almucantars for every three degrees. They further bear markings for the unequal hour lines, numbered in Roman clockwise I to XII (additive form for 4 i.e. IIII), and the astrological houses in the manner of Regiomontanus, numbered in Arabic 1 to 12 anticlockwise. The plates are laid out and marked for the following latitudes ('LAT'): 1a) XXXIX; 1b) XLII; 2a) XLV; 2b) XLVIII; 3a) LI; 3b) LIIII. The latitude is repeated in Arabic numerals on the small tongues which locate the plates in the mater. All three plates are marked with an 'F' on one side and next to it scratched an italic 'f'.
The back has the following scales (from the outside): A circular altitude scale 90? to 0?, 0? to 90?, 90? to 0?, 0? to 90?, numbered by 5? and subdivided to single degrees. This single degree scale also serves as a second circular scale, a regular division of the zodiacal signs into 12 ? 30?, anticlockwise starting with Aries at the equinoctial line, numbered by 10? in Roman numerals, divided to 5, and the usual Latin names of the zodiacal signs together with their symbols. Further inside is a calendrical scale, marked with the usual Latin names of the months divided to the corresponding number of days, numbered by 5 and further divided to single days. The equinoxes are at March 11 and September 131/2. The upper part of the space inside these circles is taken up by two horary quadrants with the hour lines numbered 1 to 12. In the lower half are two shadow scales to the base 12, each marked 'VMBRA RECTA' and 'VMBRA VERSA' and numbered by 3.
Inside the shadow scales is the maker's signature 'GEORGIVS HARTMAN NORENBERGE FACIEBAT' and the date 'ANNO MDXXXII'.
The counter changed alidade bears ornamented pointers, one of the two folding sighting vanes is missing, the other one is ornamented with a scalloped edge. The pin, washer and wedge are all replacements.
The instrument was presented by A.W. Franks in 1871 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. 115, no. 333 (with plate LIV).