I'm sure the "additional digits" denoted by X in each case will be chosen to match the current value, but perhaps they should explicitly say that. For the kilogram, the question is whether to match its current value or its 1889 value. Lacking a time machine, and being uncertain whether the master has lost weight, or the collections of copies have gained weight, the best they can really do is get somewhere in the middle of the error bar and nail it down. Since all commercial weighing ignores air bouyancy, the fourth figure is generally wrong and the fifth figure varies randomly with the weather. >From a consumer point of view, the definition is already beyond that and the value for X only matters to their fellow metrologists. It might pay to reference the current CODATA best values and uncertainies for these constants.
--- On Sun, 2/20/11, Pat Naughtin <[email protected]> wrote: From: Pat Naughtin <[email protected]> Subject: [USMA:49890] Re: New BIPM web page on the "New SI" To: "U.S. Metric Association" <[email protected]> Date: Sunday, February 20, 2011, 2:18 AM Dear Colleagues, I would like to call your attention to a new web page concerning the "New SI" at http://www.bipm.org that consolidates several papers on this topic. This is meant to be an educational body of work to prepare the public for what is intended to be a redefinition of SI base units. The actual page, which indexes and links to those documents is at http://www.bipm.org/en/si/new_si/ Implementation of that redefinition awaits refinement of some experimental determinations, but the structure of the proposed new base unit definitions are now well settled. Since this will be a rather major change, the International Committee for Weights and Measures (CIPM) and its Consultative Committee on Units (CCU) recommend that education of the public should start now, even while the refinement of the fundamental values is taking place. It is thus intended that educators, authors, and others should be prepared to incorporate the new definitions in their materials and will not be caught unaware when the actual change takes place. This new BIPM page serves the purpose of meeting that intent by providing illustrative articles. Regards, James R. Frysinger (Jim) Chair, IEEE SCC 14 Vice Chair, IEEE/ASTM Joint Committee for Maintaining SI 10 Deputy Technical Advisor, U.S. TAGs to ISO/TC 12 and IEC/TC 25 Dear Jim, Thanks for these references. However, I have a concern. When I went to http://www.bipm.org/utils/common/pdf/24_CGPM_Convocation_Draft_Resolution_A.pdf to explore the issue of the actual mass of the "new" kilogram, I found these lines: … so that new definitions of the kilogram, ampere, kelvin, and mole in terms of fundamental constants could be adopted, … the kilogram will continue to be the unit of mass, but its magnitude will be set by fixing the numerical value of the Planck constant to be equal to exactly 6.626 06X ×10–34 when it is expressed in the SI unit m2 kg s–1, which is equal to J s, … the new definitions of the kilogram, ampere, kelvin and mole are intended to be of the explicit-constant type, that is, a definition in which the unit is defined indirectly by specifying explicitly an exact value for a well-recognized fundamental constant, … the definition of the kilogram in force since 1889 based upon the mass of the international prototype of the kilogram (1st meeting of the CGPM, 1889, 3rd meeting of the CGPM, 1901) will be abrogated, … the mass of the international prototype of the kilogram m(K) will be exactly 1 kg but with a relative uncertainty equal to that of the recommended value of h just before redefinition and that subsequently its value will be determined experimentally, … the BIPM to continue its work on relating the traceability of the prototypes it maintains to the international prototype of the kilogram, and in developing a pool of reference standards to facilitate the dissemination of the unit of mass when redefined, >From these, it is not clear to me what the mass of the "new" kilogram is >intended to be. Will it be the same as the mass of the kilogram as it was in >1799 and 1887? Will it match the current mass of the kilogram? Orwill it have >some other value? Seehttp://en.wikipedia.org/wiki/Kilogram where they say: The IPK is one of three cylinders made in 1879. In 1883, it was found to be indistinguishable from the mass of the Kilogram of the Archives made eighty-four years prior, and was formally ratified as the kilogram by the 1st CGPM in 1889.[11] My concern is that there is no clear statement that the "new" kilogram will be exactly the "same" as the old kilogram. I would not like to see a public debate emerge that centres around the issue of how much "weight" the kilogram has lost or gained. My experience of journalists suggest that many journalists would find it intellectually difficult to comprehend the idea of a solid block of metal gaining or losing (say) 30 micrograms between verifications. I think that the CGPM should work toward a statement along the lines: "We have been studying the kilogram and we need to give it a better definition than 'the mass of a piece of metal stored in a bell jar in a safe in Paris'. Modern technologies need a better definition. In deciding on the better definition we will be careful to make sure that the defined mass of the kilogram will be exactly the same as it was in 1799. The mass of the kilogram will not change. Only the definition of the kilogram will change." I suppose what I am seeking is the assurance that we gain from the line: "The length of the metre has not changed since 1795 but its definition has been changed several times to match the improving technologies since then. In 1795, the metre was defined by the length of a brass bar and now it is defined in precise terms using the speed of light." 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. 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