The (a, b) fit ran over the whole merged range and the automatic resolution cutoff was
applied afterwards, so the sigma correction applied to the reflections that survive was
calibrated largely on reflections that do not. Measured on one dataset: a = 0.286
fitted over 843k reflections, 22k written. A manual --scaling-high-resolution already
restricts the population at ingest, so only the automatic path was affected.
Fit over the full range, merge, read the cutoff from that merge, refit (a, b) on the
samples the cutoff keeps, merge again. The circularity resolves by direction: the
cutoff comes from CC1/2, a correlation of the two half-set means, which the sigma scale
barely moves, so the cutoff can be read first and the sigmas calibrated on the
population it chose. One refinement, not an iteration; one extra merge pass.
Note this is invisible to the rotation battery, which passes an explicit high
resolution limit matched to XDS and so never exercises the automatic cutoff. With a
manual limit the fitted (a, b) are byte-identical to before.
The equivalent defect in the stills / offline --scale path is untouched; it is a
different engine and needs its own validation.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 5
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