[Om] Questions about representing units

Professor James Davenport jhd at cs.bath.ac.uk
Sat Feb 21 19:28:24 CET 2009

On Sat, February 21, 2009 1:46 pm, Jonathan Stratford wrote:
> In response to the questions left for me below.
>>BTW, does your unit converter
>>(http://klein.activemath.org:90/~jonathan/units/converter.php) support
>> such compound units for which no explicit symbol has been defined?
> Yes, it can cope with many of these (it can't cope with all of them as the
> algorithm's by no means perfect). For some reason, I can't get the online
> version to load, but the following (just picking 2 examples from my
> testing)
> work both with the version that was in my dissertation, and my local copy
> of what I think is on klein.activemath.org (it's slightly updated):
> 17.3 millimetre per nanosecond sqrd to mile per hour sqrd
> 6 ounce inch per minute sqrd to kilogramme metre per second sqrd
>>Then, a final question about that unit converter: I can convert hours to
>>minutes, but for minutes to seconds, and hours to seconds, it tells me
>>> The two units were known, but found to be different dimensions. Please
>>> supply a definition for the units to reconcile this difference,
>>> remembering to ensure the new definition has a different name.
>>> 1 hour to second is incalculable.
> I'm not certain offhand what the problem with seconds is, but I would
> suspect it is because the unit "second" appears in both units_metric1 and
> units_time1, and the algorithm's picking the one in metric, then failing
> to
> find the path through to units_time1. My lookup algorithm returned the
> first
> unit it came across that matched the name "second", and then if the other
> unit was a different dimension, there was no way to go back and look for
> another unit. I mentioned it in my dissertation:
> "It is unclear whether the unit second should be removed from either of
This certainly needs tidying up.

James Davenport
Visiting Full Professor, University of Waterloo
Hebron & Medlock Professor of Information Technology and
Chairman, Powerful Computing WP, University of Bath
OpenMath Content Dictionary Editor
IMU Committee on Electronic Information and Communication

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