^Cardarelli, F. (2003). Encyclopaedia of Scientific Units, Weights and Measures. Their SI Equivalences and Origins. London: Springer. pp. 7. ISBN978-1-4471-1122-1.
^ abcClarke, F.W. (1891). Weights Measures and Money of All Nations. New York: D. Appleton & Company. p. 50.