[3] NIST Handbook 44 - 2013 Edition, Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices,
Appendix B. Units and Systems of Measurement Their Origin, Development, and Present Status, 2.2.5. Status of the Metric System in the United States., Measurements expressed in U.S. statute miles, survey feet, rods, chains, links, or the squares thereof, and acres should be converted to the corresponding metric values by using pre-1959 conversion factors if more than five significant figure accuracy is required. ページB-7
