To further belabor the point, I looked up the measured 1893 relationship between the meter and yard based on bronze #11, the official yard of the United States (SP 447): 1 yd = 0.914 399 80 m, which results in 1 " = 25.399 994 mm.
Had Mendenhall approximated this relationship rather than the reciprocal, he certainly would have chosen 1 yd = 0.9144 m and 1 in = 25.4 mm, rather than the clumsy relationship 1 yd = 0.914 401 83 m and 1 in 25.400 051 mm (which looks better in the reciprocal). ----- Forwarded Message ---- From: John M. Steele <[email protected]> To: [email protected]; U.S. Metric Association <[email protected]> Sent: Fri, May 13, 2011 6:49:41 AM Subject: Re: [USMA:50458] US Customary Well, not quite the same as "mesures usuelle" which were visibly rounded from their prior values. If you don't accept fractions of a millimeter, there is no difference between 914.4 mm and 914.401829 mm; unless you can measure micrometers over this distance, there is no difference. As I have pointed out before, the Mendenhall inch was a good idea conceptually, but a very poor idea technically. The inch at the time was known to a much better value than the crudely rounded value Mendenhall made into law. The "official" value of 1959 differs by only a few tenths of a part per million from the measured value in 1893, and by 2 ppm from the Mendenhall value. Had Mendenhall been thinking metrically, he would have defined the inch in terms of millimeters (and rounded suitably) instead of defining the meter in terms of inches. Had he done so, and used the measured value of the time, he certainly would have rounded at 1" = 25.4 mm. I view it as equivalent to the mistaken redefinition of the liter from 1901 to 1964 as 1 kg H20 @ 4 °C instead of 1 dm³, later abrogated. ________________________________ From: Pat Naughtin <[email protected]> To: U.S. Metric Association <[email protected]> Sent: Thu, May 12, 2011 10:20:23 PM Subject: [USMA:50458] US Customary On 2011/05/13, at 08:18 , John M. Steele wrote: "It should also be considered to make the story accessible to international readers, who generally have a poor understanding of US Customary." Whatever "US Customary" is! I understand that US Customary is fully metric at this time in 2011 since all the old measuring words (such as inch, ounce, pint, mile, pound, and ton) have all been defined by metric system units since 1959 or 1893. Currently, US Customary measuring words have the same status that Napoleon's "mesures usuelle" had between 1812 and 1839. US Customary is just a way to use new definitions -- that never existed before 1893 or 1959 -- to protect some old measuring words to which many, perhaps most, of the citizens of the USA have become accustomed and think they understand. In short (to paraphrase John Steele) many, perhaps most, citizens of the USA also "have a poor understanding of US Customary." Cheers, Pat Naughtin LCAMS Author of the ebook, Metrication Leaders Guide, see http://metricationmatters.com/MetricationLeadersGuideInfo.html Hear Pat speak at: http://www.youtube.com/watch?v=_lshRAPvPZY PO Box 305 Belmont 3216, Geelong, Australia Phone: 61 3 5241 2008 Metric system consultant, writer, and speaker, Pat Naughtin, has helped thousands of people and hundreds of companies upgrade to the modern metric system smoothly, quickly, and so economically that they now save thousands each year when buying, processing, or selling for their businesses. Pat provides services and resources for many different trades, crafts, and professions for commercial, industrial and government metrication leaders in Asia, Europe, and in the USA. Pat's clients include the Australian Government, Google, NASA, NIST, and the metric associations of Canada, the UK, and the USA. See http://www.metricationmatters.com/ to subscribe.
