Re: redefining the standard kilogram

In article <5kpPj.58006$QC.54917@xxxxxxxxxxxx>, Paul Danaher
<paul.danaher@xxxxxxxxxxx> writes:

Uh-oh - to quote:
"Electrical power can be related to the Planck constant, defined as
the ratio between the frequency of an electromagnetic particle such as
a photon of light and its energy. This experimental method of defining
the kilogram relies on selecting a fixed value for the Planck
constant, which is currently determined experimentally based on the
fixed value of the kilogram artifact."

The circularity is disturbing.

No. CURRENTLY the kilogram is fixed and Planck's constant is derived.
This is one alternative. The other is to reverse the situation. In the
past, the meter was fixed and the speed of light was measured. Now the
situtation is reversed. Same idea.

There's also a nice Fermilab colloquium presentations by Richard Steiner
(NIST) on "How Measuring the Planck Constant gets to an Electronic Kilogram
Standard" on 1 Aug 2007: search for Steiner in
http://www-ppd.fnal.gov/EPPOffice-w/colloq/colloq_06_07.html

Avogadro's number looks better here ...

In a sense, yes, it's more straightforward. On the other hand, the idea
of fixing some constants of nature and deriving the standard measures
from them, as the meter is derived from the speed of light, also has its
attractions.

.