Paul,
I'm going to answer this on the list since others likely will have the
same questions.
When you get further into the document, you will see that it points out
the watt balance as being essential for macroscopic determinations of
mass at the primary local standards level.
Yes, this would fix the Avogadro number for everyone. Recall that IUPAC
and IUPAP are involved in this effort!
Jim
On 2014-01-06 08:20, Paul Trusten wrote:
Jim, this is quite exciting! I shall have to sit down and compare the current
SI Brochure with the draft.
It seems like a clever strategy to define the constants in terms of the base
units, so that the base units then become defined by the constants. I don't
know if I'm asking the right question, but here goes. Does this definition plan
eliminate the need for the watt balance and other experiments on redefining the
kilogram, since the Planck constant henceforth shall be exactly defined?
Also, once the BIPM defines the Avogadro constant exactly, does that definition
indeed become binding on physics and chemistry? It never occurred to me until
now that the keepers of the world measurement system might also be the keepers
of definitions that affect disciplines beyond metrology. Perhaps this is why
consultative committees exist. I don't really know how this actually works.
Paul
Paul Trusten, Registered Pharmacist
Vice President and Public Relations Director
U.S. Metric Association, Inc.
Midland, Texas, USA
+1(432)528-7724
www.metric.org
trus...@grandecom.net
On Jan 5, 2014, at 16:42, James <j...@metricmethods.com> wrote:
Dear USMA Folks,
The next edition (the ninth) of the SI Brochure is likely to reflect, as you
know, the shift to using seven exactly defined natural constants as the basis
for the SI. The process of defining values for those constants in appropriate
units effectively defines the SI base units. Currently, the likely date of
publication of the final draft for edition 9 will be in 2018, give or take.
In anticipation of this, work has progressed in re-writing the SI Brochure. I
have posted here previous drafts of small sections of the new material in the
past, as well as some underlying documents that discuss the nature of that
shift of emphasis.
Now, a major portion of the new version of the Brochure's first three chapters
is available, courteously provided to us by Barry Taylor (NIST, CCU). You may
view the draft at, and download it from:
http://www.bipm.org/utils/common/pdf/si_brochure_draft_ch123.pdf
I have, so far, carefully read the first several pages (of 29) and have skimmed
the rest. Clearly this is a major rewriting of the Brochure and not a tweak to
update it. That is, it is a fresh start and not a patch.
So far, I am greatly impressed. The text flow starts "ab initio" in the field
of metrology and quickly develops the system from there. The flow of information is
smooth and clear to the careful reader -- at least one experienced in the SI. And one
**should** read it carefully. Like any good technical writing the information content is
concentrated; no blathering appears in this document and every word is essential.
I will continue my careful study of this document. But in the meantime I would like to
put it out here on the list for you to see. Hopefully this will start a lively and
relevant discussion. One criterion that I think we should gauge it by is how accessible
it is to the neophyte, the student, the general but decently educated member of the
public. In short, is it "teachable"? So far as I have read it, I think that it
is.
Now, let's hear your opinions!
Enjoy!
Jim Frysinger
Chair, IEEE SCC14
