% units
551 units, 41 prefixes
You have: pint
You want: imperial pint
* 0.83267413
/ 1.20095
Ok, well enough. Lots of people forget that these are different, but
it's a thing and it's good that units knows about it. (Maybe it should
be less US-centric, but that's not what I'm looking at tonight.)
This is also reasonable:
You have: pint
You want: brpint
* 0.83267248
/ 1.2009524
Except wait, they're not quite the same...
You have: imperial pint
You want: brpint
* 0.99999802
/ 1.000002
I assume that's a rounding bug and not intentional.
This, however, seems problematic:
You have: imperial pint
You want: british pint
* 1.2009476
/ 0.8326758
I assume the word "british" in units.lib is meant for use as an
adjective in some other other context. However, I'm wondering what,
given this:
You have: british
You want: 1
* 1.000002
/ 0.999998
That is, it's almost but not quite 1, probably because of rounding.
Meanwhile this doesn't work:
You have: pint
You want: metric pint
units: Unknown unit 'metric'
which given the way units works isn't surprising, but this could and
doesn't:
You have: pint
You want: metricpint
units: Unknown unit 'metricpint'
(where a metric pint is 500 mL)
Meanwhile things like this shouldn't be allowed:
You have: lightyear
You want: imperial lightyear
* 0.83267413
/ 1.20095
You have: lightyear
You want: british lightyear
* 0.999998
/ 1.000002
since "imperial" is correctly only useable as a modifier on certain
volume units.
Then, units.lib defines a constant fuzz == 1 that appears to be used
to tag definitions that are not precise, but it's used inconsistently
and not always correctly (e.g. it's attached to c and should not be)
and units itself doesn't know about it or what it means so it serves
no actual purpose currently.
So, some propositions:
(a) Dimensional analysis is great but it seems like we ought to have
some additional typing rules to prevent misuse of adjective units;
(b) units ought to be able to track the number of significant digits
in its definitions and computations and print accordingly;
(c) units.lib should get some editorial attention. Does anyone know
what "british" is supposed to be there for?
(d) deep chrome green
--
David A. Holland
dholl...@netbsd.org
