Danielson, Dennis (2006). The First Copernican: : Georg Joachim Rheticus and the Rise of the Copernican Revolution. New York: Walker & Company. ISBN978-0-8027-1848-8., Kindle edition location 1424-31, "Rheticus's other graduation speech, in April 1542, accompanied the awarding of only ten new M.A. degrees, compared with twenty-two in February. However the recipients included the illustrious Johannes Crato, who would prove himself a loyal friend to Rheticus and who went on to become the personal physician to three successive emperors."
