Re: [boost] Re: quantity libraries

From: Matthew Austern (austern_at_[hidden])
Date: 2001-09-05 11:52:44

"Peter Schmitteckert (boost)" wrote:
> 
> Salut,
> 
> > > TOPIC:  Some "constants" are experimental numbers with finite precision,
> > >
> > > rather than defined values; they may have to be updated when experiments
> > >
> > > get better.
> > >
> > > There seem to be two choices: the values are either compiled-in or
> > > read in at run-time.
> breaking compatibility of your results.
> 
> > There's also a third choice: assume them to have value of 1,
> > devise your unit system accordingly, and avoid the whole mess.
> 
> a small comment:
> 
> working with the strange system where c = h/2pi = 1 has the advantage
> that your calculations are independent of measurements of natural constants.
> Suppose you want to build a new atominc clock, which is 1000 times more
> precise than older ones, but to convert the result into seconds you
> have to apply arithmetic with h. You may now face the problem that your
> new device is more accurate than the numerical value of h. therefore
> it might be preferable to work in such a system.

Actually, c is one of the few constants where this is not a problem.
In the SI system the meter is defined in terms of c.  By definition,
c is exactly 2.99792458 x 10^8 m/s.

(But yes, in the SI system hbar does have finite precision.)

                        --Matt