The instrument is based on the Sicilian astrolabe in the Museum of the History of Science, Oxford, which was probably made around 1300 (inventory no. 40829). However, it is designed as a simple north astrolabe. In contrast, the original is a combined north-south instrument with equinoctial rete.
This astrolabe is only set up for the latitude of 45° North. Still, it can be used between 42° (Rome) and 48° (Paris) without significant error. It is kept simple. Azimuth circles and the lines of the unequal hours have been omitted. On the other hand, the back shows the ecliptic and calendar circles (15th century), in contrast to the Sicilian astrolabe.
The back also features the diagram of the unequal hours, a shadow square and an alidade (without reticle, so unsuitable for measuring altitude).
The complete description of the instrument as PDF for download
