Taylor, B.N. and Thompson, A. (Eds.). (2008a). The International System of Units (SI). Appendix 1, p. 70. This is the United States version of the English text of the eighth edition (2006) of the International Bureau of Weights and Measures publication Le Système International d' Unités (SI) (Special Publication 330). Gaithersburg, MD: National Institute of Standards and Technology. Retrieved 18 August 2008.