units symbols

[Dubernet-Tuckey marie lise]

   Dear All,
 The following information might be relevant to the present discussion.
A division at NIST (National Institute of Standards & Technology) is
currently working on modeling UNITS (project UnitsXML). You can find
all information on the link below:

 http://www.mel.nist.gov/msid/sima/07_ndml.htm

      best regards,
          marie lise dubernet

>
> Dear data modelers,
>
> I attach to this mail a comparison of the symbols used
> for units in different sources: IAU recommendations,
> VizieR, HEASARC and the GNU software Units.
>
> The reason for this was to try to study to which extent
> the representation of units was compatible among those
> various sources, and see if we can solve the issue of
> representing units in the VO with a minimum cost. You'll
> find a set of URLs at the end of the spreadsheet for these
> sources.
>
> For the IAU, I used symbols in Tables 1, 2, 5, and also
> table 6 which contains deprecated ones.
>
> I'm *not* discussing here the issue of multiples/submultiples
> (see IAU table 4, HEASARC table 3),
> nor the rules for composition of symbols into a complex unit
> expression (e.g. square meters written as m2, m^2 or m**2).
>
> Note that the symbol expressions are CASE SENSITIVE (h and
> H are different!).
>
> I outlined in the spreadsheet:
> green: same symbol everywhere
> yellow: only trouble with GNU
> gray: upper/lowercase difference
> red: discrepancy
>
> The first conclusion is that most of the basic symbols are
> identical in the 4 compared sets. There are only 2 discrepancies:
> - rad is not recognized for radians in GNU Units
> - the unit for electric resistance is  Ohm ohm Omega ?
>
> As we go to more exotic quantities, I noted a few issues
> along the way:
> - The IAU recommendation for year symbol (a) is only used in VizieR;
> the other use yr
> - The definition of the year itself is ambiguous, e.g. between VizieR
> and GNU (how many seconds, julian or not?)
> - IAU lists symbols I've not seen in VizieR or at HEASARC and did not
> list here: c for «cycle », and the deprecated: mu, cc, Gal, E, Oe
> - the above 'c' is ambiguous with speed-of-light!
> - Heasarc also uses: Crab, chan, bin, voxel
> - GNU knows very little about astronomy-specific things
>
>
>    Do you think this kind of comparison could be a starting point
> for defining a common unit representation for the VO?
>
> Sebastien.
>
> PS: the 2 attached file are identical: one for OpenOffice 2.0,
> the other for MS-Excel.
>
>