<div dir="ltr"><div>I think the authors waffled on the issue, on purpose.<br>There are three statements that are relevant here:<br>1. FITS writers <i>should</i> use the IAU recommended SI units<br>2. Angstrom and erg are <i>deprecated in the IAU list</i><br></div>3. Angstrom and erg are in a list of <i>allowable units</i><br><div>My interpretation is that Angstrom and erg are not<br></div><div>deprecated in FITS, but neither are they on the preferred<br></div><div>list of units: the combination of the three statements<br></div><div>says that they are allowable, but you <i>should</i> not use<br></div><div>them (i.e., less strong than deprecated), where <i>should</i><br></div><div>should be interpreted in its customary way in that use<br>of these units constitutes <i>conditional compliance</i> with<br>the standard.<br><br></div><div> - Arnold<br></div></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature"><div dir="ltr">-------------------------------------------------------------------------------------------------------------<br>Arnold H. Rots Chandra X-ray Science Center<br>Smithsonian Astrophysical Observatory tel: +1 617 496 7701<br>60 Garden Street, MS 67 fax: +1 617 495 7356<br>Cambridge, MA 02138 <a href="mailto:arots@cfa.harvard.edu" target="_blank">arots@cfa.harvard.edu</a><br>USA <a href="http://hea-www.harvard.edu/~arots/" target="_blank">http://hea-www.harvard.edu/~arots/</a><br>--------------------------------------------------------------------------------------------------------------<br><br></div></div></div>
<br><div class="gmail_quote">On Tue, Nov 4, 2014 at 2:31 PM, Steve Allen <span dir="ltr"><<a href="mailto:sla@ucolick.org" target="_blank">sla@ucolick.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">On Tue 2014-11-04T20:18:26 +0100, Thomas Robitaille hath writ:<br>
<span class="">> Thanks for your reply - but just to be clear, are angstrom and erg<br>
> *actually* deprecated in the FITS standard? That is, should a strict<br>
> writer emit a deprecation warning? It wasn't obvious to me whether the<br>
> fact the units are deprecated in McNally 1988 also means that the units<br>
> are deprecated in FITS?<br>
<br>
</span>The header of Table 4 says erg and Angstrom (to be strict, note the<br>
capital A) are "allowed".<br>
<br>
These rules are somewhat haphazard, in particular note that annum "a"<br>
is allowed and therefore peta-annum "Pa" is an explicit exceptional<br>
forbidden case to avoid ambiguity with pressure measured in pascal "Pa".<br>
<br>
If a FITS writer software package wants to be used by the instrument<br>
building teams that I know then it had better have an option for not<br>
emitting warnings for units like "degC" and "degF".<br>
<div class="HOEnZb"><div class="h5"><br>
--<br>
Steve Allen <<a href="mailto:sla@ucolick.org">sla@ucolick.org</a>> WGS-84 (GPS)<br>
UCO/Lick Observatory--ISB Natural Sciences II, Room 165 Lat +36.99855<br>
1156 High Street Voice: <a href="tel:%2B1%20831%20459%203046" value="+18314593046">+1 831 459 3046</a> Lng -122.06015<br>
Santa Cruz, CA 95064 <a href="http://www.ucolick.org/~sla/" target="_blank">http://www.ucolick.org/~sla/</a> Hgt +250 m<br>
<br>
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