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
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clients include the Australian Government, Google, NASA, NIST, and the
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