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

[Mcglynn, Thomas A. (GSFC-6601)]

Demitri Muna wrote:

>> 2. Angstrom and erg are /deprecated in the IAU list/
>
> Deprecated means (to me) that you should not be using feature X, but 
> if you do (and you can) /don't be surprised if in the future if your 
> file that uses feature X no longer works (which in this case could 
> mean the file can be read but will not be written out the same way as 
> above).
>
> That said, I don't see why an updated FITS format can't attach any 
> unit (e.g. anything defined in astropy.units) to any column (barring 
> ambiguity of course).
>
>
Given FITS' rule of once FITS, always FITS, I don't believe that's the 
appropriate meaning for deprecation
in this context.  Indeed the standard explicitly defines deprecate as:
> Deprecate: To express disapproval of. This term is used to refer
> to obsolete structures that should not be used in new FITS
> files but which shall remain valid indefinitely.
stating that deprecated usages are to remain valid forever.  We may wish 
to be careful not to mix in meanings of deprecate from other contexts, 
e.g., in programming languages and such.

Regards,
Tom McGlynn