This elegant astrolabe, constructed for use in England, shows a close resemblance to the astrolabes traditionally associated with the Parisian maker Jean Fusoris (1365-1436). It has been assumed, therefore, that this instrument originated from his workshop in Paris. However, several characteristics of this astrolabe deviate from Fusoris, most notably the different style in letters and numbers, and so it is unlikely to have come from his workshop. The obvious similarities with Fusoris may lie in the fact that he came to London and Norwich in 1415, where he might have shown someone else how to make them. The Museum of the History of Science in Oxford (inventory no. 47.674) contains a very similar astrolabe that was almost certainly constructed by the same maker, whose identity remains anonymous at present.

The throne is very simple and low, merely acting as a link between the combination of shackle and suspension ring and the limb. The limb is made of two semi-circles, which are riveted to the mater. The inside of the mater is engraved with a stereographic projection for 50º (this engraving is cruder than on the rest of the instrument giving the impression that it is a later addition). There is one plate for latitudes 52º/51º 34' (those of Oxford and London). The rete is cut for 22 stars with star pointers of the wavy-flame type. On the back of the instrument is a degree scale, zodiac scale and calendar scale, inside of which is a shadow square. The upper right quadrant has an equal hour diagram which is unusual for Western astrolabes of this date. 'Ex dono magistri Johannis Thornoe' is engraved on one arm of the rule: probably the name of the owner.