The World Factbook APPENDIX G :: WEIGHTS AND MEASURES, "At this time, only three countries - Burma, Liberia, and the US - have not adopted the International System of Units (SI, or metric system) as their official system of weights and measures."
MacLean, R.W. (4 June 1957). "A Central Program for Weights and Measures Canada". Report of the National Conference on Weights and Measures, Volumes 41–45. Forty-second National Conference on Weights and Measures. Washington, D.C.: アメリカ合衆国商務省 – アメリカ国立標準技術研究所 (NIST). pp. 44–49.
Barbrow, Louis E.; Judson, Lewis V. (October 1963) [March 1976]. “7. The Mendenhall Order”. Weights and Measures Standards of the United States: A brief history – NBS Special Publication 447. US Department of Commerce, National Bureau of Standards. pp. 16–20. LCCN76--60005. http://physics.nist.gov/Pubs/SP447/sec07.pdf19 April 2013閲覧。
[2](PDF) Louis E. Barbrow and Lewis V. Judson,"Weights and Measures Standards of the United States A brief history", 1976, Appendix 5. The United States Yard and Pound, Refinement of Values for the Yard and the Pound, pp30-31.
Barbrow, Louis E.; Judson, Lewis V. (October 1963) [March 1976]. “7. The Mendenhall Order”. Weights and Measures Standards of the United States: A brief history – NBS Special Publication 447. US Department of Commerce, National Bureau of Standards. pp. 16–20. LCCN76--60005. http://physics.nist.gov/Pubs/SP447/sec07.pdf19 April 2013閲覧。