# [Om] Questions about representing units

Christoph LANGE ch.lange at jacobs-university.de
Sat Feb 21 00:51:41 CET 2009

```Dear James, dear Jonathan, dear all,

here are some questions about representing units in OpenMath and about your
unit converter.

An easy one first:  I didn't find a concrete example for prefixing, but may I
assume that the following is correct?

<!-- 1 kilometre -->
<OMA>
<OMS cd="arith1" name="times"/>
<OMI>1</OMI>
<OMA>
<OMS cd="units_ops1" name="prefix"/>
<OMS cd="units_siprefix1" name="kilo"/>
<OMS cd="units_metric1" name="metre"/>
</OMA>
</OMA>

Then, how about compound units?  There are some convenience symbols like
metres_per_second, but what do we need them for?  Wouldn't it make more sense
to do without them (as you suggested to do without metre_squared) and write

<!-- 1 m/s -->
<OMA>
<OMS cd="arith1" name="times"/>
<OMI>1</OMI>
<OMA>
<OMS cd="arith1" name="divide"/>
<OMS cd="units_metric1" name="metre"/>
<OMS cd="units_metric1" name="second"/>
</OMA>
</OMA>

(http://klein.activemath.org:90/~jonathan/units/converter.php) support
such compound units for which no explicit symbol has been defined?

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.

Is there any better place for reporting this bug?

BTW, we are planning to add a unit conversion service to our active document
https://jomdoc.omdoc.org/ticket/254 if interested in further details.

Christoph

--
Christoph Lange, Jacobs Univ. Bremen, http://kwarc.info/clange, Skype duke4701

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