[wfc] Checksum proposal

[Eric Greisen]

I was mislead by the header From line in the original post: send
messages simple to wfc at nrao.edu.

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I have read the Checksum proposal 2002-02-27 version and, on first
reading, am inclined to vote NO.

1. Unless the rules have changed, "standards" are to be published in
A&A.  The present manuscript is not in a form for - or even properly
written - for that journal.

2. Exactly what my software is supposed to do to implement this is
unclear - not the encoding which is described in detail, but the
principles.  This goes in part bak to point 1 - an HDU is what?  Is
each attached extension a separate HDU with separate DATASUM and
CHECKSUM keywords?  The manuscript does not say - and I ought to be
one of the more knowledgable readers of the MS.

3. Now, how do I implement this?  It appears that I read and translate
my data to FITS form three times, actually writing it out on the 3rd
pass
    a. To get DATASUM
    b. To get CHECKSUM
    c. To write the output file.
Computers are now faster, but this seems still rather a serious
overhead.  Again - point 1 - I should not have to ask this question.

It appears to me that this is an internal convention for those systems
that store their data internally in FITS format and are able to update
single header keywords as they go.

The FITS community also needs to look at another issue - whether all
of the "conventions", even those that are widespread, ought to be
"standards".  If something is a standard, then most widespread
software systems ought to support it.  If it is a convention, we have
a greater leeway.

I might change my mind if the paper were properly written.  I need to
be convinced that I need this thing, that my two's complement computer
cares about negative zero, that I might reasonably be able to
implement it, etc.

Eric Greisen