The astrolabe is a multi-functional instrument which enables the user to perform such diverse tasks as timekeeping at day and night, surveying, determining latitude and casting horoscopes.Some of the markings on this instrument show the Flemish influence on early English makers: for example, the star names are given with their magnitudes and their corresponding astrological planetary temperaments. The mater bears the markings for a quadratum nauticum ('nautical square'), used by mariners for navigational calculations, and the back shows the universal projection as described by Gemma Frisius in his treatise on the 'Catholic astrolabe' of the mid-sixteenth century.It is possible that this astrolabe once belonged to Henry, Prince of Wales (1594-1612) as an inscription in a later hand on the mater suggests, but the case bearing the monogram and Henry's coat of arms may be a later addition.