The upper part of the plate has a compass, with the cardinal points named 'Septentrio', 'Oriens', 'Meridies', 'Occidens', and magnetic deviation marked. Surrounding the compass box is a degree scale in two quadrants, divided to ten and to five, subdivided to one degree, numbered from 10 to 90 by 10 with 0 at the top. Below is the inscription 'Declinatio magnetis', and the signature 'Pragae fecit Erasmus habermel'. The centre of the plate is engraved with hour lines and latitudes. The latitude lines, inscribed 'Numerus elevationis' twice, are concentric circles engraved and numbered from 10 to 85 by 10. The three main lines with the numbering are dotted. The hour lines are engraved every quarter-hour and numbered with a dotted line from 4 to 12 to 8. Near the outside border are the inscriptions 'Horae post meridiem' and 'Horae ante meridiem'. The remaining space between the hour lines, the circles enclosing them and the compass is filled with decoration of fruits and foliage. The circle itself is a ring, inscribed with the names of the main winds 'Notus', 'M libonot<us>', 'Libonotus', 'V. libonot<us>', 'Noto Libicus', 'M Aphrics', 'Aphricus', 'V Aphrics', 'Zephirus', 'M Corus', 'Corus', 'V Corus', 'Boro Libicus', 'M Circius', 'Circius', 'V Circius', 'Septen:<trio>', 'V Aquilo', 'Aquilo', 'M Aquilo', 'Bora Peliotes', 'V Caecias', 'Caecias', 'M Caecias', 'Subsolanus', 'V Eurus', 'Curus', 'M Eurus', 'Nota Peliotes', 'V Phoenix', 'Phoenix', 'M Phoenix'. The corners of the plate are decorated with geometrical motifs and arabesques typical of Habermel. On this side of the plate is a folding quadrant arm, inscribed 'Numerus Elevationis poli', with the wind vane at the top, and from which is hanging the plumb bob. The arm, which is decorated, has teeth on the upper side. On the other side the arm has a scale of altitudes, corresponding to the teeth, with one tooth per degree. The scale is numbered from 20 to 85 by five.

The other side of the plate has a volvelle. The top rotating part of the volvelle is engraved with a sun effigy and an hour scale, divided to the quarter hour, numbered from 1 to 24. On the index arm, with a decorated end, is a zodiac scale inscribed 'Ortus solis Horae ab Or{tus} Quan:<titas> nocti'. The zodiac scale is divided to ten degrees, numbered by ten from 10 to 30, with the zodiacal symbols.

The volvelle underneath has a scale of hours, divided to the quarter hour, numbered from 1 to 24. The index is inscribed 'Occas.<us> solis Horae ab Oc{casus} Quan:<titas> diei' and with the same zodiacal scale. Around this volvelle the plate is engraved with hours, divided to the quarter-hour, numbered 1 to 12 twice. Around these hour lines latitude lines are engraved by two degrees, numbered 10 to 90 by 10. Every 10 degrees the line is dotted. The cardinal points are named 'Septentrio', 'Oriens', 'Meridies', 'Occide<n>s'. Around the latitude lines is a zodiac scale, with the symbols of the zodiacal signs and their names in Latin. The scale is divided to 10 and to 5 degrees, subdivided to one, and numbered from 10 to 30 by 10. Surrounding it is a calendar scale, divided to one day, numbered from 10 to 30 or 31 or 28 as appropriate. The equinoxes are at 23rd September and 21st March. The names of the months are engraved in Latin. In use, both brass arms are adjusted symmetrically so that the position on the zodiac scale corresponds to the latitude of use. The times of sunrise in Italian hours and of sunset in Babylonian hours, corresponding to the length of the night and of the day, can be read on the corresponding volvelles.

The spandrels are decorated with geometrical motives and arabesques typical of Habermel. A brass arm on the left hand side serves to keep the latitude arm on the other side of the plate.

The instrument was bequeathed by Croft Lyons in 1926 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. 24, no.21.