King, David A. (2005). "The Sacred Geography of Islam". In Koetsier, Teun; Luc, Bergmans (eds.). Mathematics and the Divine: A Historical Study. Elsevier. pp. 162–178. ISBN0444503285.
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.
Young, Cynthia Y. (2018). Precalculus. Wiley. p. 620.