A characteristic feature of Arab-islamic astronomy during the Middle Ages is the promotion and tremendous growth of practical astronomy which was in turn manifested primarily by the establishment of scores of observatories in West-Central Asia, from Abbasid Caliph al-Māmūn (813-833) to the Turkish king Murād III (1574-1595), and by the production of copious literature on astronomical Tables (the zījes) as well as on astronomical instruments (ālāt al-rasad). The enormity of the literature on the

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... latter could be gauged by the list of extant works as given by Matvievskaya and Rosenfeld (1983) in their recent Biobibliography: 349 treatises on astrolabes, 138 on sine-instruments, 81 on quadrants, 4 on sextants and octants, 41 on armillary spheres and celestial globes, 77 on sundials and again 77 on "other instruments"—in all 767 treatises. As a matter of fact the instruments developed by Arab-islamic astronomers could be broadly classified into four groups: a) Time measuring instruments (e.g. sundials, shadow quadrants), b) Angle measuring instruments for astronomical parameters (e.g. armilla of various kinds, dioptre and parallactic rulers), c) instruments for transformation of system of coordinates and/or solving nomographical problems (e.g. astrolabes, quadrants,dāstūrinstrument), d) Mathematical instruments for evaluating trigonometric functions, (e.g. sinequadrants). Apart from the fourth and the most important of all, the astrolabe, which in turn embodies all the four groups of instruments to a certain extent, works on "other instruments" were compiled in almost every century (down from 9th to 18th A.D.), also by well-known Arab-Islamic astronomer-mathematicians.