King, David A. (2005). "The Sacred Geography of Islam". In Koetsier, Teun; Luc, Bergmans (eds.). Mathematics and the Divine: A Historical Study. Amsterdam: Elsevier. pp. 162–78. ISBN0-444-50328-5.
King (2005, p. 169). The calculations were as accurate as could be achieved under the limitations imposed by their assumption that the Earth was a perfect sphere.