The de-novo centering gate promoted to a centred lattice only when the mean
signed <I/sigma> of the centering-absent class was <= 0.5x that of the present
class. Weak / low-energy data carry a positive intensity floor (background /
profile leakage) that lifts <I/sigma> of the genuinely-extinct class to ~1.5-2.3
instead of ~0; when the present class is itself weak that additive floor inflates
the ratio past the bound and the true centering is missed. An I-centred cubic
crystal recorded at 5 and 13 keV sat at ratio ~0.57 and stayed primitive P2_1 3,
while the same crystal form at 6 keV (stronger data) correctly merged as I23 - an
energy-dependent space group for one physical crystal.
Add a second, floor-independent acceptance path OR'd with the mean-ratio: the
centering-absent class's strong-reflection rate (violations / absent) versus the
present class's own strong rate. A false centering (absent as strong as present)
fails both arms; a true weak centering passes the rate arm. Battery SG sweep vs
XDS: the low-energy datasets now adopt I23, and no crystal is newly over-centred.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 4.8
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