I'd like to know how they were able to measure the yard to 8 decimal places way back in 1893. What instrument did they use?
Jerry ________________________________ From: Pat Naughtin <[email protected]> To: U.S. Metric Association <[email protected]> Cc: U.S. Metric Association <[email protected]> Sent: Sunday, April 5, 2009 9:53:54 PM Subject: [USMA:44420] The_inch_is_no_cinch!_=97_formerly_= =?WINDOWS-1252?Q?_Re:_Even_with_=22dual,=22_you_can't_please_eve?=rybody On 2009/04/06, at 12:24 AM, John M. Steele wrote: I'd like to comment on this idea of the changing inch as it illustrates the problem of being too liberal in rounding a conversion factor. Measured data should be rounded consistent with its measurement accuracy. However, conversions are either declared values (legal definitions) or the highest accuracy a lab is capable of. Destroying that accuracy is frought with with risk. The UK had their own problem with the "incredible shrinking yard." However, according to NIST SP447 (downloadable from their site) p. 21, the US yard prototype was measured in 1893 just before the Mendenhall order. It was determined to be 0.914 399 80 m, only 0.22 parts per million different from the International foot adopted in 1959. Yet, the Mendenhall order established a rounded value 1 m = 39.37 inches (equivalent to 0.914 401 83 m) which led to a greater difference with the UK yard, and became so entrenched that we are still cursed with it today in the form of the US Survey foot. They knew it was wrong, but the chose to adopt a definition that had good enough accuracy for commercial purposes from the Metric Act of 1866. The Mendenhall order freed us from separate physical standards for Customary measure, which is a good thing. However, the wrong choice of value, and a worse choice than they were capable of making at the time has not worked out entirely well. In any case the difference between Survey and International foot is only 2 parts per million, affecting volumetric measure 6 ppm, so it hasn't changed much. I disagree that we should round conversion factors willy-nilly to a "nice" round number when we know better. Dear John, Thanks for these thoughts. My comment is contained in a new title for this subject: 'The inch is no cinch!' Cheers, Pat Naughtin 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/ or to get the free 'Metrication matters' newsletter go to: http://www.metricationmatters.com/newsletter to subscribe.
