This is probably one of the oldest astrolabes in the NMM collection and one of the earliest known European astrolabes to have survived. Thus, it remains an interesting example despite the fact that it was made rather crudely and has very imprecise star positions. The instrument displays a clear influence of Islamic astrolabes, for example the rippled throne. The fact that there is a calendar on the back of the astrolabe shows that it was probably copied from a Western Islamic astrolabe rather than an Eastern Islamic one. The spelling of the stars on the rete is a mixture of Europeanised Arabic and Latin, as is standard on medieval European astrolabes. There is sufficient evidence to suggest that the style of this instrument is Andalusian, but its precise place of origin currently remains unresolved.

The throne is cast in one piece together with the limb, which is soldered to the mater. The inside of the mater is inscribed with a stereographic projection as are both sides of the two plates. The rete is crudely fashioned and the equinoctial bar is counter-changed in the middle. Around the rim on the back of the instrument are scales for the zodiac, degrees and calendar. What remains is divided in four quarters, all left unengraved apart from the lower right one, which accommodates a shadow square. The alidade, pin and roundrel are all later additions.