Stan, With respect to SI, there is one and only one *coherent* SI unit for each physical quantity. e.g. kilogram for mass, newton for force, joule for energy, watt for power, etc. The Mg is certainly *not* a coherent SI unit of mass, neither is a kilowatt (kW) a coherent SI unit of power.
Applications of SI prefixes to SI coherent units do, in fact, make multiples and submultiples of coherent SI units incoherent with respect to all the other coherent SI units. The kilogram is the only exception for historical reasons. SI prefixes are certainly destroyers of coherence in favor of scaling SI coherent units up or down to enable convenient expressions of numerical values without exaggerating implied precisions. How does your definition of "coherence" differ from the above CGPM concept of coherence? Gene. ---- Original message ---- >Date: Wed, 25 Jun 2008 08:01:24 -0400 >From: "Stan Jakuba" <[EMAIL PROTECTED]> >Subject: Re: [USMA:41217] Re: tonne >To: <[EMAIL PROTECTED]>, "U.S. Metric Association" <[email protected]> > >Gene: >I suggest you check on the definition of "coherent." And perhaps also on >what a prefix is as it has nothing to do with coherence. >Stan > >----- Original Message ----- >From: <[EMAIL PROTECTED]> >To: "U.S. Metric Association" <[email protected]> >Sent: 08 Jun 24, Tuesday 13:33 >Subject: [USMA:41217] Re: tonne > > >> Stan, >> >> More simply; A "tonne" is a "metric ton" is 1 000 kg in coherent SI. The >> Mg has never been widely used and is not coherent or appropriate for >> masses of 1 000 kg and more. >> I object to promotion of the Mg on grounds of incoherence with the SI unit >> of mass, the kilogram. >> >> Gene.
