Dear all, (01)
Here are some answers and comments to some parts of some of yesterday�s
mails (taken in temporal order)
---
Gunther S: �Nowhere in my practical experience of working with units in
the sciences do I ever see a qualification of units.� (02)
IJ-answer: I firmly believe you, but I think this absence of
qualifications is due to the fact that in each practical case the context
automatically creates a qualification as background knowledge. But general
metrology can have no such pre-given context qualifications.
--- (03)
Joe C: �I would not agree that "many units are unambiguously tied only to
one kind-of-quantity".� (04)
IJ-answer: Depends on what we mean by �many�. Surely, all the six base
property quantities of the SI are (but not �amount of substance�).
--- (05)
Matthew W: �Could you give me a unit (or two) that you think only applies
to one kind-of-quantity, and I'll see if I can identify another? (06)
IJ-answer: m (length), kg (mass), and t (duration).
--- (07)
Gunther S (to Pat H): �so we agree that 1 N.m = 1 N.m when we talk about
units and there is no such thing as "N.m moment of force" as a unit?
There is of course the Quantity moment of force 1 N.m, but the unit is
still N.m without knowing anything about torque vs. energy.� (08)
IJ-comment: Every real unit presupposes a scale for a kind-of-quantity; a
unit with no reference at all to a scale or quantity is meaningless. What
I have proposed to call a �nominal unit�, is a unit that necessarily
refers to other units, i.e., to real units with scales for
kinds-of-quantities.
--- (09)
Gunther S: �The VIM speaks about Quantities and measurement and a little
bit about Units. The SI speaks a lot about Units. I don't think that
either one argues that Units contain the detail of the Quantities.� (010)
IJ-comment: I think you are wrong. VIM�s definition 1.9 says: measurement
unit = real scalar quantity, defined and adopted by convention, with which
any OTHER QUANTITY OF THE SAME KIND CAN BE COMPARED. Definition 1.10 says:
base unit = measurement unit that is adopted by convention FOR A BASE
QUANTITY. The SI brochure says (p. 103): The terms quantity and unit are
defined in VIM. That is (at least in my interpretation), both VIM and the
SI are stating the view that �Units presuppose the detail of the
Quantities�. Or in my words, once again: every real unit presupposes a
scale for a kind-of-quantity.
--- (011)
Best,
Ingvar (012)
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