Michael Lindgren (Craig G. McKay, trans.), Glory and Failure: The difference engines of Johann Müller, Charles Babbage, and Georg and Edvard Scheutz (Cambridge, Massachusetts: MIT Press, 1990), pages 64 ff.
„Charles Babbage”. The MacTutor History of Mathematics archive. School of Mathematics and Statistics, University of St Andrews, Scotland. . Arhivat din original la . Accesat în .
„Charles Babbage”. The MacTutor History of Mathematics archive. School of Mathematics and Statistics, University of St Andrews, Scotland. . Arhivat din original la . Accesat în .