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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