The universal plate devised by Ali Ibn Khalaf al-Saydalini is a universal instrument of the 11th century al-Andalus. Among the Alfonsine Libros del Saber de Astronomia,there is a book which includes the treatise on its construction, the author of which is Isl)aq b. Sld (Rabiyag)a collaborator of the King, and the treatise on the use which seems to be a translation from a lost original Arabic written by Ibn Khalaf. Although both treatises have been partially studied previously, there were many questions still unsolved. This paper presents new data regarding the morphology of the instrument, confirms the consistency between the description of the shape of the rete as described in both treatises, which had been questioned, and gives two chapters analysing the use of the matter in conjunction with the rete
