Subject: Another comment on George's and Lorella's FITS units draft

From: "Don Jennings -- COSSC" <[email-masked]>
Date: Fri, 16 Apr 93 08:25:04 -0400

My comment on the units draft is similar to that of Paul Barrett and concerns
the relative importance of the eV, keV, MeV, GeV and even PeV units.

While X-ray astronomers usually think in terms of keV, Gamma ray astronomers
prefer MeV and GeV (and occasionally PeV) when describing the energy of
photons. To be fair to astronomers of both wavelengths, I propose that we
either do as Paul Barrett suggests and promote eV units to table 2 (recommended
units), demote keV to table 3 (allowed but discouraged) and add GeV (PeV) to
table 3, OR we promote all of these units to table 2.

If the FITS readers can be made to understand the 'keV' string, then it takes
little extra effort to make them understand 'MeV', 'GeV' and 'PeV'.

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From: "Don Jennings -- COSSC" <[email-masked]>
Date: Fri, 16 Apr 93 15:41:09 -0400

>little extra effort to make them understand 'MeV', 'GeV' and 'PeV'.

This morning my tired brain forgot to include 'TeV' in the list of desired
energy units.

Also, how about adding nanometers (nm) to the list of allowed units in
table 2. It is at least as useful as angstroms, if not more politically
correct in the SI sense.

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From: [email-masked] (William Pence)
Date: Thu, 22 Apr 93 12:56:32 -0400

Here's my input on some of the units issues:

 - I prefer 'bin' over 'pixel as a unit of length but would be willing to
support both.

- Negative powers:  I think it is a small matter for parsers to be able
to support the '/' character, so would prefer allowing which ever
form is more concise or intelligible to the user.

- Numerical factors as units:  I can see a use for this in cases where
the values could over or underflow a variable on typical machines.  So
I find '10**(44) erg /s' acceptable, but would not like to see this
usage required to eliminate the use of SI prefixes.  While it is a bit
disagreeable, I think all the standared SI prefixes need to be
supported since that is what people are used to seeing.  As was
previously mentioned the TSCAL and TZERO keywords may be useful in some
cases, but this in itself does not solve the underflow problem.
Finally, I don't seem much advantage to Jonathan's idea of having
an additional TUSCLnnn keyword since FITS readers would then have
to search for 2 keywords, not just one..  I'd rather see all the unit 
information contained in the single TUNIT keyword, 

-Bill Pence