Ibn Yunus and Mathematical Techniques
reached a high level of sophistication in spherical trigonometry. For example, his Hakimi Zij
contains a table of sines for each 010° of arc, computed to 4 sexagesimal digits, where the values are rarely in error by more than +/-2 in the fourth digit (in keeping with the standard in Islamic works, the trigonometric functions used by Ibn Yunus are functions of arcs computed for radius 60). The Zij
also outlines several hundred formulae for use in spherical astronomy
(some of which are equivalent) and at least one numerical example is usually given for each formula.
D.A. King, 'Ibn Yunus', in The Dictionary of Scientific Biography
, New York 1970
John North, The Fontana History of Astronomy and Cosmology, London 1994