Proposal to disallow SU from _diffrn_refln_counts_* data names

[James H]

Dear Core DMG,

During the course of recent discussions (see
https://www.iucr.org/__data/iucr/lists/ddlm-group/msg01704.html and
citations within) it was noted that the _diffrn_refln_counts_* data names
are used both to report a measured value (and thus exact, with no SU) and
an estimate of the true count rate (a real number with SU). As a refresher,
these data names were intended to record the raw measured counts for
background and peak using a point detector. None of these data names appear
in the COD or wwPDB, and in general have been rendered almost obsolete by
the advent of area detectors.

I propose subtly changing the definition for these data names to remove the
expectation that a SU could be attached to them. In this I am following the
lead of the powder dictionary, which separated the two meanings by
introducing equivalent real-valued "intensity" data names with associated
SU, and for the "count" data names stated that:

      Standard uncertainties should not be quoted for these values.
      If the standard uncertainties differ from the square root of
      the number of counts, _pd_meas.intensity_* should be used.

Essentially, I propose adding a similar paragraph to the definitions for
_diffrn_refln_counts_*. In our case, _diffrn_refln.intensity_net performs
the role of intensity and would not be affected by this change.

A related longer-term project that any of you are most welcome to take up
is to define data names that would be useful in capturing how peaks are
extracted from area detector images.

Please comment. If comments are generally supportive, or absent, the
details of this change will be worked out in the Github repository (
https://github.com/COMCIFS/cif_core) which you are all welcome to follow
and contribute to, of course.

best wishes,
James.

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