Pat H wrote: (01)
> Chris Partridge wrote:
>
>> Pat,
>>
>> The direct/indirect distinction was raised by Matthew and can be
>> found in
>> ISO 15926. Matthew or David can give you the latest links if you
>> cannot
>> google it. (02)
> Direct vs. indirect UNITS is one notion, coming from metrology, which
> I kind of grok and understand we must live with, though I don't think
> there is very much to say about it in a units ontology other than to
> provide it as a classification without any definition. Direct vs.
> indirect PROPERTIES is not a notion from metrology, and I am not happy
> living with it, and I have not yet seen anyone explain what it is
> supposed to mean. I suspect it has no meaning at all. Direct vs.
> indirect QUANTITIES I presume means simply, quantities measured using
> direct vs. indirect units. (if this presumption is wrong, please
> someone enlighten me.) But please, let us not get units, properties
> and quantities all confused with one another. (03)
Please, Chris, Matthew, or David, expalain what the ISO distinction
between direct and indirect properties amounts to. I think I am even more
confused than Pat. Neither VIM nor the SI contains any distinction between
direct or indirect units or properties, but they contain a distinction
between base units and derived units. In the philosophy of measurement, on
the other hand, there is since long a distinction between direct and
indirect measurement. In H. Kyburg's book "Theory and Measurement" the
chapter about direct measurement (5) starts as follows: (04)
"By 'direct measurement', I mean measurement which does not depend on the
measurement of any other quantity." (05)
And the chapter about indirect measurement (6) starts as follows: (06)
"Temperature, density, and velocity are commonly cited as examples of
quantities that admit only of indirect measurement. Indirect measurement
is taken to involve empirical laws or definitions." (07)
The Wikipedia entry on ISO 15926 gives no explanation of the distinction
between direct and indirect properties. It merely says: "indirect property
type (e.g. the class "cold locked rotor time")." So once again, please,
explain the distinction. (08)
Best,
Ingvar (09)
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