The whole celestial sphere
In its standard form, the astrolabe is provided with several latitude plates. The instrument can only be used accurately in places whose latitude matches one of the plates. It is therefore limited in scope. The ambition to design a 'universal' instrument, based on a complete projection of the celestial sphere stems from a desire to overcome this limitation and to extend the 'cosmographical' range of the astrolabe. This astrolabe uses the 'universal lamina' described by Islamic mathematicians in 11th-century Toledo, where a special form of rete rotates above a horizontal projection of the entire celestial sphere.
Astrolabe, North African, 13th century? (Inv. 41122)