I don't blame you, it was a rhetorical challenge. But it illustrates that there are changes that matter to "the man in the street" and changes that matter only in a metrology lab. In between, there are some changes that may matter to high-precision industry.
To the man in the street, the inch has never changed, so the argument rings a bit hollow. The change is orders of magnitude below the errors risked in buying a new measurement tape at the hardware store. Obviously it has changed in the metrology lab, and at the request of high-precision industry. While you flog the 2 ppm change in the inch, you assert the metric system has never had such changes. For the meter, that is true (apart from the abortive quadrant of the earth, about a 200 ppm error). However, the liter has changed twice, from 1 dm³ to 1 kg of water at 4 °C in 1901, and back to 1 dm³ in 1964, While not formally part of the SI, it is allowed for use with the SI and is an important unit in commerce affecting the man in the street. Per the SI Brochure, this change in volume is of the order of 28 ppm. The linear change of 2 ppm in the inch produces a 6 ppm volumetric change in the US gallon and bushel, considerably less significant. NOTE: Accuracy of fill legislation is generally around 1% or worse, I have never seen any tighter than 0.1% (1000 ppm) so 28 ppm isn't all that important to the man in the street either. Still, it indicates the SI has made changes when deemed necessary, too. You are probably correct that the reconciliation of the inch and pound slowed the demise of Customary/Imperial units. The use of decimals rather than common fractions and "all inches" rather than feet and inches in industry or decimal feet (to 0.01) in surveying have also helped mask the worst features of Customary/Imperial. In the US, Customary volumes are often given in "all ounces" as well as gallons/quarts/pints/ounces breakdown. These conventions mask the messy mixed base conversions for most consumers. That aside, it is a pity that while they picked a sane value for the inch (25.4 mm) they didn't pick a sane value for the pound, 453.6 g. It is only 17 ppm different from the chosen pound and is sufficiently divisible by 7 and 16 to yield a 28.35 g ounce and 64.8 mg grain. The man in the street never would have noticed. As an aside, the Mendenhall inch clearly existed as it was specified in the order. However, there is no Survey inch. It is a trick question because surveyors don't use inches. However, it is like units de-legislated in the UK, no longer defined legally, but the definition lingers in old reference material and people's minds. ________________________________ From: Pat Naughtin <[email protected]> To: U.S. Metric Association <[email protected]> Sent: Mon, January 31, 2011 2:00:17 AM Subject: [USMA:49708] Re: [SI] A mole hill into Himalaya On 2011/01/31, at 09:00 , John M. Steele wrote: I continue in my challenge to Pat that I defy him to actually survey the difference between International and Survey feet with available field equipment. Dear John, I have no intention of taking up your challenge to continue any detailed metrological discussion. I do intend, however, to sometimes refer to the idea that the lengths of feet vary as a point to support metrication programs. Consider this thought: The metre has been the same length since 1795. However such things as inches, feet, yard,, miles, nautical miles have had various lengths from time to time during the same period. This is a true statement to support a mind-set shift to considering the relative methods of the metric system compared to previous old and variable measuring methods. It is a metrication statement - not a metrological statement. To my mind the 1959 retrofitting of the inch, the foot, the yard, the mile, the ounce, the pound, etc. as pseudo metric "units" has been an unmitigated disaster. It gave credibility to these old measuring words to which they had no historical right. Suppose that the 1959 decision had not been made. We would then be in a position to argue like this: You can use the metric system for detailed drawings or you could use the Imperial inch, the Canadian inch, the Imperial inch, the USA customary inch, or the Mendenhall inch (which might not exist so use a tenth of a foot). The metric inch of 1959 has more credibility than any of these and so it is a direct impediment to metrication programs -- pity! 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.
