The mater consists of three layers of brass soldered together. The rim is engraved with common hours numbered from I to XII twice with XII at the zenith, and with a scale of degrees divided to 2 degrees by alternate shading, numbered from 10 to 90 by 10. The inside of the mater is blank.
THE rete has 28 star pointers of the 'wavy flame' type, all named in Latin. The ecliptic has a scale of degrees on the edge, divided to the degree and numbered from 10 to 30 by 10. The names of the zodiacal signs are engraved in Latin. The tropic of cancer line is divided on the edge every 2 degrees, numbered from the cardinal west, from 10 to 360 by 10. The east-west line is counterchanged three times.
There are three plates, kept in place by a stud on the inside of the mater, fitting in small holes on the plates. Two of them are engraved with east-west and meridian line, both tropics and equator line, almucantars every 3 degrees numbered from 9 to 90 by 9, azimuth lines every 10 degrees numbered by 10, twilight line, unequal hour lines numbered from 1 to 12, astrological houses numbered from I to XII. The plates are for the latitudes 41 and 43, 45 and 48 as punched on the plates themselves. The third plate is engraved on one side with a map of the known world, with the tropics engraved 'TROPICO DEL CANCRO' and 'TROPICO DEL CAPR', the equator engraved 'AEQVINOCTIALE', and places engraved 'EVROPA', 'SPA<GNA>', 'AFFRICA', 'ARABIA', 'OCEANO', 'ASIA', 'TRAPOBANA', 'MOLVCCHE', 'INDIA', 'NVOVA SPAGNA', 'AMERICA', 'CANAR<IE>'. The sea is dotted. The first meridian is approximately through the Canary Islands, and the longitude lines are engraved on the plate and numbered on the rim every 10 degrees from 10 to 360. Latitude lines are engraved and numbered every 10 degrees from the north pole to 20 degrees south of the equator. The back of this plate has on the rim a scale of hours numbered from 1 to 12 twice with 12 at the zenith. Further to the centre is a scale of degrees divided in 4 quadrants to 2 degrees, numbered from 10 to 90 by 10 with 90 at the zenith. Further to the centre is another scale of degrees divided to 2 degrees and numbered from 10 to 30. The symbols of the zodiacal signs are engraved correspondingly. Further to the centre is a calendar scale divided to 2 days, numbered by 10 days from 10 to the last day as appropriate. The abbreviated names of the months are engraved. On the bottom left quadrant of the central part is a shadow square divided to 1 and numbered by 3, with the letters 'R' and 'V' punched. The top left quadrant is engraved with unequal hour lines, numbered from 2 to 9 and from 1 to 12, engraved respectively 'HO POT MER.' And 'HO AN ME'. The bottom right quadrant is engraved with a scale on the edge, divided to 1/3 by alternate shading and numbered from 1 to 6 counterclockwise and 7 to 12 clockwise.
The back of the mater is engraved with a scale of degrees on the rim, divided in four quadrants to 2 degrees, numbered from 10 to 90 by 10 with 0 at the zenith. The rest of the plate is engraved with a Rojas projection, 23 stars engraved and 16 named, the poles engraved 'POLVS ARTICVS' and 'POLVS ANTARTICVS'. The symbols of the zodiacal signs are engraved. Unequal hour lines are engraved with dotted lines, numbered from 1 to 12, with further lines every 1/3 hour. They are also engraved 'HORE ANTE MERIDIEM' and 'HORE POST MERIDIEM'. On the back of the mater fits a diametral rule, engraved with an unequal scale divided on the edge every degree and numbered from 10 to 360 by 10 degrees, from the centre of the instrument from 10 to 90, then to 270, to 260.
Suspension is by ring, shackle and throne. The throne is elaborated with scrollwork, and on a small case on the front is a compass. On the back are a blank coat-of-arms and the date '1568'.
The alidade is counterchanged and has two double sights. It is engraved with a scale of latitudes divided by 5, numbered from 20 to 90 by 10 on one arm, and with hours from 2 to 12 ( 'OC') and from 11 to 1 ( 'OR') on the other arm. The ends of the alidade are decorated.
A cylindrical wedge keeps the pin in place.