Re: [boost] Re: SIunits and quantity library concerns

From: Kevin Lynch (krlynch_at_[hidden])
Date: 2001-10-05 13:31:03

"George A. Heintzelman" wrote:
> 
> > Jonathan H Lundquist wrote:
> > >
> > > >   From: "Eric Ford" <eford_at_[hidden]>
> > >
> > > >> Quantities can be measured in bins, cartons, bags, etc., all of
> > > >> which are user-defined units of measure.
> > > >
> > > > These can all be considered pure numbers.  You're counting something.
> [snip]
> 
> > > I think they have to be more than pure numbers, they're units of
> > > measure in that bins can be converted to cartons, etc.  But the
> > > conversion factors do depend on the qualifiers.
> 
> > I wouldn't have said "pure numbers" like Eric did, but I agree with what
> > he is saying.  The quantities being measured here are "dimensionless"
> > and "unitless", and can decay into "pure numbers" in the appropriate
> > circumstances, but I would agree that they are not _currently_ pure
> > number.
> 
> I disagree. If we develop tags, then I think these things have an SI
> unit of Amount<>, which can be measured in units of moles, or
> individual items. Anything can be measured in this units, not just the
> atoms and molecules of chemistry.
> 
> And as is very natural with other types of SI unit Amount<>, the
> conversion factors are important. Treating it this way may make some of
> these things clearer.
> 
> George Heintzelman
> georgeh_at_[hidden]
> 

Alright, I might be able to buy that argument.  Like I said, I'm not
sure what I'm missing just yet, and this may be one of those things. 
Just to make sure that I understand, you're saying that "number of
things" has is a quantity of type Amount<>, and the unit here is "number
of cartons".  So it is not "unitless", but Amount<> is still
"dimensionless" since it is a counting "unit".

-- 
-------------------------------------------------------------------------------
Kevin Lynch				voice:	 [phone]
Physics Department			Fax: [phone]
Boston University			office:	 PRB-565
590 Commonwealth Ave.			e-mail:	 krlynch_at_[hidden]
Boston, MA 02215 USA			http://physics.bu.edu/~krlynch
-------------------------------------------------------------------------------