The limb of the astrolabe is divided twice from 1 to 12 and four times from 0 to 90. The rete displays 27 stars, represented by points bored into the base, and accompanied by their names.

The zodiac circle bears the names of the signs of the zodiac in Latin. The pointer is divided from 80 to 10, with the inscription 'LATI. SEPTEMTIO', and 10 to 23, with the indication 'LATI. MERI'.

The back of the astrolabe displays its limb divided into 4 quadrants, each of 90 parts, then a circle X to XXX, repeated 12 times, followed by the names of the signs of the zodiac in Latin, the days of the month and the names of the months in Latin. The upper part of the central area of the back of the instruments bears the hour lines 1 to 6, 7 to 12 (12 coincides with the diameter), which frame the engraving of a two-headed eagle with outstretched wings.

The lower part of the back of the astrolabe bears the half shadow square with the inscriptions: 'VMBRA VERSA' and 'VMBRA RECTA', repeated twice. Under the half-square is the signature 'GEORGIUS HARTMAN NOREM.BERGE FACIEBAT ANNO 1545'.

The alidade is provided with reclining sights, with two holes and notches to help the instrument to be aimed accurately.

The inside of the mater lacks any indications. It contains three plates, calibrated for latitudes 45 and 49?, 42 and 39?, and 53 and 51?. The instrument is very accurately made, and the engravings are both precise and elaborate.