The mater comprises a thin sheet of brass and attached limb. Soldered shaped and pierced throne; no shackle or suspension ring. The limb has a scale of hours 0 to XII twice, with Roman numerals, with XII to the right and left and VI at the throne, divided to 1 hour, subdivided to 20 minutes and to 4 minutes. Inside the meter is a tablet of horizons for every 5 degrees, numbered by 10.
One plate engraved on one side only with a terrestrial map, from the north pole to the 'TROPIQVE DE CAPRICORNE', with names of oceans and continents, also 'LE PERV' (Peru) and 'IAVA', tropics and equator. The map has various figures, the monogram 'ARN' and the motto '?SIC ? VITA ? PER ? HORAS'. On the edge of the plate is a degree scale 0 to 360 anticlockwise, divided to 10, subdivided to 10/6, numbered by 10. The plate is free to rotate.
The back has an outermost degree scale, 90 to 0 to 90 to 0 to 90, divided to 5, subdivided to 5/6, numbered by 5; in two quadrants the disposition of the digits in alternate numbers is reversed. Within this is a zodiacal scale with names and symbols for the signs, each with a 30-degree section divided to 10 and using the outer scale for subdivision to 10/12, numbered by 10 with Roman numerals. These scales are marked 'CERCLES CONCENTRIQVE [sic]'. Within that is an eccentric calendar scale with the names of the months, with various mistakes, each with a scale of days divided to 5, subdivided to 1, numbered to 5 as appropriate, and marked 'CERCLES EXENTRIQVE [sic]'. The upper half of the central space has an unequal hour diagram in two quadrants, with hour lines numbered 1 to 12 and 12 to 1, and lines for half-hours. In the central circle of this diagram is a perpetual calendar and a lunar volvelle and aspectarium. The lower half has a double shadow square with scales 0 to 12 to 0 to 12 to 0, divided to 3, subdivided to 1 with alternate hatching, numbered by 3, marked 'VERSEE LVMBRE DROICTE VERSEE'. In the centre of the shadow square is the same monogram and motto as on the geographical plate; outside it are stars and the moon with a face in profile.
Modern screw and nut, alidade and index.
See R. T. Gunther, The Astrolabes of the World (2 vols, Oxford, 1932), vol. 2, p. 357