VOUnit for solar density or metallicity?

[Mark Taylor]

On Wed, 1 Jun 2022, Norman Gray wrote:

> 
> Markus, Marco and all, hello.
> 
> I don't have a strong position on the question of using eg SFUs in preference to '10**-22W.m**-2.Hz-1', but I do recall that, during the initial discussion of the VOUnits spec, the point was made (in that case in the context of jupiterMass) that 'SFU' has at least some value as documentation, which the equivalent in SI base units doesn't.  The VOUnits strings are intended to be machine-readable, but they're not intended to be _only_ machine readable.  I think we say something to that effect in the standard, but the point could be made more strongly, that the units string should or could be usable as a label on a graph, where something like 'SFU' would be preferable to the expansion of it.

I agree with this in principle.  In practice much the most common use 
of VOUnits (strings appearing in places where VOUnits are required 
or recommended) will be as human-readable text rather than 
machine-parseable tokens, so my feeling is that VOUnits should err 
on the side of inclusivity and attempt to accommodate unit 
representations that people actually want to use which are well 
defined and not obviously nasty - so yes to SFU, no to Sun.

Exactly how best to accommodate that sort of thing is another question,
it depends rather on how many items fall into this category.
SFU could just be included in the current VOUnits update, but
perhaps that would miss a number of equally respectable units
we haven't thought of.  People can always write 'SFU' (with quotes)
to satisfy the VOUnits grammar and human readability.

Mark

--
Mark Taylor  Astronomical Programmer  Physics, Bristol University, UK
m.b.taylor at bristol.ac.uk          http://www.star.bristol.ac.uk/~mbt/