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From: Paul A. Bristow (boost_at_[hidden])
Date: 2003-10-24 03:38:22

I deliberately put 'everyone' in quotes because there are some strange people
about ;-)

But I take your point - not everyone can live with SI only. So a framework that
allowed many units systems, of which SI is just one, would be ideal. But it
needs devising.


Paul A Bristow, Prizet Farmhouse, Kendal, Cumbria, LA8 8AB UK
+44 1539 561830 Mobile +44 7714 33 02 04

| -----Original Message-----
| From: boost-bounces_at_[hidden]
| [mailto:boost-bounces_at_[hidden]]On Behalf Of Matthias Troyer
| Sent: Wednesday, October 22, 2003 8:51 PM
| To: Boost mailing list
| Subject: Re: [boost] Re: Physical Quantities revisited
| On Wednesday, October 22, 2003, at 08:51 PM, Paul A. Bristow wrote:
| > I (and others) also expressed the prejudice that all are kept as their
| > base
| > unit, now that 'everyone' is using at least 64-bit doubles in their
| > calculations
| > (which is enough to keep everyone except the astronomers in the
| > exponent range.
| > And the significand precision available (15-ish decimal digits) is
| > ample for all
| > physical measurements.
| I want to disagree here. I know particle physicists who use singe
| precision (float) numbers in some of their calculations. If instead of
| a common choice of units where hbar=1 one uses SI unites, where hbar is
| about about 1e-34, there will be problems. Even worse problems come
| when hbar^2 is needed.
| Since for many calculations I do in quantum mechanics a natural set of
| units is where hbar, the speed of light, and the charge of the electron
| are set to one, I would not like to be forced to use SI units.
| Matthias
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