[fitsbits] Celsius unit in FITS keyword comments

[Steve Allen]

On Thu 2016-03-03T11:42:45 +0100, Richard J. Mathar hath writ:
> What is the recommended unit that goes into the bracket of the
> FITS keyword line if the datum is a temperature in Celsius?

My FITSBITS inbox gives me the impression that it is March, so it must
be the season for endless discussions about the merits of daylight
saving time.  Units in FITS keyword values is much the same.

Quickly looking through the units in active use for recent telescopes
and instruments at Lick and Keck I find many instances of "degC", and
also
MiB             => mebibytes (2^20 bytes)
percent
%
encnt           => encoder count
encnt/s         => encoder count per second
dacnt           => digital to analog converter count
degrees C
gpm             => gallons per minute
milliamp
Volts
UNIX seconds    => since 1970, not counting leaps
seconds         => (probably the same as above)
unknown         => some sensor from some vendor measuring some quantity
min             => minutes of time since some meteorological event

These units are generally for the values of various engineering
quantities that describe the status of the hardware and environment
during construction, debugging, diagnosis during ongoing operation.
Those values are expressed in the units that the off-the-shelf sensors
supply, and with which the development engineers are familiar.
Nevertheless, they are important for investigating often-subtle
systematic errors which affect the resulting science data, so they
can be included into the FITS headers.

In this arena the FITS WCS papers, and the standard, have to remain
using the word SHOULD rather than MUST.  This is not a subject where
authoritarian sentiment nor reasonable arguments about simplicity for
parsers of the FITS files can get an agreement for change.  If the
IAUFWG were to hold a vote about requiring only SI units, and if I
were to enquire the rest of the instrument engineering and
construction teams how to vote, I would end up translating their
two-word negative response into simply "No".

--
Steve Allen                 <sla at ucolick.org>               WGS-84 (GPS)
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