Dear Ed, (01)
> David Leal wrote:
> >>> There are at least two ideas of what the members of "1.3 kg"
> >>> including:
> >>> a) the members are mass tropes of different individual
> >>> of matter;
> >>> b) the members are different individual quantities of matter.
> I wrote:
> >> I don't know what David's (b) means. I would have said the
> >> of the equivalence class designated "1.3kg" are either:
> >> a) 'mass tropes' of different individual things, or
> >> b) measurements of the 'mass tropes' of individual things.
> Matthew West wrote:
> > MW: I would say neither of these, but the individual things
> > The measurements are of these.
> > E.g. My lump of cheese is a member of the 1.3Kg equivalence
> This may be true of 'mass', but it doesn't generalize. The person
> Barkmeyer is not a member of the 180cm equivalence class. The
> height of
> EdBarkmeyer is a member of the 180cm class. But the waist size of
> EdBarkmeyer is a member of a different class (predictions of one of
> former students notwithstanding). In a similar way, the existence
> of a
> thing may be a member of one duration class, while some other
> is a member of a different duration class. (02)
MW: Firstly, I did not know we had introduced a rule that said that you
could only belong to one class, or that different temporal parts of you
could not belong to different classes, or that different spatial parts
of you could not belong to different classes. (03)
MW: Also you get close what in ISO 15926 was distinguished as direct and
indirect properties. Roughly, a direct property is something simple that
can be directly measured. Then there are other properties, where this
does not apply. "Maximum Allowable Working temperature" for example is
not a temperature (try going up to a furnace tube and measuring it
directly), but is expressed in terms of a temperature. (04)
MW: I agree with the rest below. (05)
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> > MW: <snip> I think it is important to
> > distinguish two concepts:
> > 1. The mass something has,
> > 2. A measurement of the mass something has.
> I think this is exactly the same pair as David's (a) and (b) above,
> the substitution of "something" for
> "individual quantity of matter", and my (a) and (b) above is the
> with a slightly different substitution. It seems to me that we are
> in violent agreement, except that we can't agree on the spelling of
> "some thing".
> > We should not be choosing to be interested in one or the other,
> > both.
> This is in fact exactly the point. The VIM says we cannot know the
> first; we can only know the second. But, as Pat points out, this
> doesn't mean that the first doesn't exist and cannot be idealized.
> Whatever we do in this regard must be consistent. The way in which
> intend to use the "equivalence class" notion to define magnitudes
> supposes ideal and exact quantities, independent of measurements.
> OTOH, the typical business and scientific usage is about
> with respect to a scale that has a "granularity" -- it makes
> distinctions and assigns "quantity value" names only to the
> intervals, which are "equivalence classes" of a somewhat different
> kind. Matt's lump of cheese has a mass of 1.3kg on a scale in
> which the
> next choice is 1.35kg or 1.4kg and finer distinctions are
> The reason they are meaningless is all about measurement,
> and tolerance. It is not useful to state that the mass of the
> cheese is
> exactly 1.31415926536 kg, because the scale isn't nearly that good
> it won't change the price.
> So I agree we need to think about both, but we need to see the use
> and requirements to decide how much of this to axiomatize.
> Edward J. Barkmeyer Email: edbark@xxxxxxxx
> National Institute of Standards & Technology
> Manufacturing Systems Integration Division
> 100 Bureau Drive, Stop 8263 Tel: +1 301-975-3528
> Gaithersburg, MD 20899-8263 FAX: +1 301-975-4694
> "The opinions expressed above do not reflect consensus of NIST,
> and have not been reviewed by any Government authority." (09)
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