[fitsbits] Question on angstrom and erg units in FITS standard

[Arnold Rots]

I think the authors waffled on the issue, on purpose.
There are three statements that are relevant here:
1. FITS writers *should* use the IAU recommended SI units
2. Angstrom and erg are *deprecated in the IAU list*
3. Angstrom and erg are in a list of *allowable units*
My interpretation is that Angstrom and erg are not
deprecated in FITS, but neither are they on the preferred
list of units: the combination of the three statements
says that they are allowable, but you *should* not use
them (i.e., less strong than deprecated), where *should*
should be interpreted in its customary way in that use
of these units constitutes *conditional compliance* with
the standard.

  - Arnold

-------------------------------------------------------------------------------------------------------------
Arnold H. Rots                                          Chandra X-ray
Science Center
Smithsonian Astrophysical Observatory                   tel:  +1 617 496
7701
60 Garden Street, MS 67                                      fax:  +1 617
495 7356
Cambridge, MA 02138
arots at cfa.harvard.edu
USA
http://hea-www.harvard.edu/~arots/
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On Tue, Nov 4, 2014 at 2:31 PM, Steve Allen <sla at ucolick.org> wrote:

> On Tue 2014-11-04T20:18:26 +0100, Thomas Robitaille hath writ:
> > Thanks for your reply - but just to be clear, are angstrom and erg
> > *actually* deprecated in the FITS standard? That is, should a strict
> > writer emit a deprecation warning? It wasn't obvious to me whether the
> > fact the units are deprecated in McNally 1988 also means that the units
> > are deprecated in FITS?
>
> The header of Table 4 says erg and Angstrom (to be strict, note the
> capital A) are "allowed".
>
> These rules are somewhat haphazard, in particular note that annum "a"
> is allowed and therefore peta-annum "Pa" is an explicit exceptional
> forbidden case to avoid ambiguity with pressure measured in pascal "Pa".
>
> If a FITS writer software package wants to be used by the instrument
> building teams that I know then it had better have an option for not
> emitting warnings for units like "degC" and "degF".
>
> --
> Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
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