Olaf Pedersen: «The and the Traditions of Medieval Latin Astronomy: A Tentative Interpretation.» S. 59–76 i Owen Gingerich og Jerzy Dobrzycki (red.): . Wrocław: Ossolineum, 1975. Olaf Pedersen: «In Quest of Sacrobosco», i , 16 (1985): 175-221. Lynn Thorndike: Sphere. Chicago: Univ. of Chicago Press, 1949.