# Boost :

From: Paul A. Bristow (pbristow_at_[hidden])
Date: 2001-04-23 17:20:58

I have concluded that we MUST have a way of storing with the units
the uncertainties (for the measurement-minded)
(or intervals to the mathematically-minded).

(For a few, uncertainties are zero - by definition conversion of inch to mm
is 25.4 exactly.)

But for most physical constants and conversion factors
they are + something - and often - something different.

This makes it more complicated!

Do we wait for an interval system,
or just provide three values:

lower limit, mean, most likely, central value, upper limit?

And are limits 95% confidence or what?

Actual values are available from NIST collections, for example.
But we need to decide a packaging method.

As I have painfully discovered with math_constants,
achieving consensus on this is not so easy!

Paul

Dr Paul A Bristow, hetp Chromatography
Prizet Farmhouse
Kendal, Cumbria
LA8 8AB UK
+44 1539 561830
mailto:pbristow_at_[hidden]

> -----Original Message-----
> From: Peter Schmitteckert (boost) [mailto:boost_at_[hidden]]
> Sent: Friday, April 13, 2001 11:18 AM
> To: boost_at_[hidden]
> Subject: Re: [boost] arithmetic type wrapper
>
>
> Salut,
>
> > >
> > > meters m = meters (10) + meters (20); //ok
> > >
> > > feet f = feet (5) + feet (10); // ok
> > >
> > > meters (10) + feet (20); // oops, compile-time error
> >
> > Wouldn't it be more useful to define conversions between feet
> and meters?
> >
> And the result type should be ? Living in Europe I would always convert
> to SI units. Maybe it would be better to use explicit conversion
> then, e.g.
> meters( feet(20) )
>
> Best wishes,
> Peter
>
> P.S:
> By the way, how should one handle the case of redinitions of units?
> With most of the units we're quite safe for normal life,
> but the defintion of the kilogramm is still based on the prototype
> in Paris and it may happen in the future that the defintion will be
> based on natural constants, like the meter is based on the
> definition of time
> using vacuum light speed. This won't change any conversion between
> feet and meter, but there might be a change in the last few
> digits of some
> constants.
>
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