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Three comments about "observations" (just to point out a few
other aspects of "observations", etc):

1.  Reflections with zero intensities are useful in refinement, even
if they don't contribute much to Fo maps.  They provide important
restraints on the electron density.

2.  I've slowly discovered that some data reduction programs count
partials as "measurements".  I understand why you'd do that, but
it's a tad confusing when the number of measured reflections gets
so large.

3.  And another slow realization on my part is that our cryo-EM
colleagues have a wonderful way to increase their number of
observations.  They pick an arbitrary (or at least it looks that way
to my un-trained eyes) grid in reciprocal space to sample their
diffraction pattern perpendicular to the 2-d crystals.  There must
be some guidelines for acceptable choices for that sampling interval,
but if they change it a little, they can change their number of
observations by large numbers.

Ron

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