Two guards catch a per-frame scale far below the run median. Both then invented a value for it -
one substituted the run median, the other set corr = 1 and merged the frame "unscaled". For a frame
whose scale really is 1/17402 of its neighbours', asserting 1 is worse than asserting nothing, and
it is the assertion that does the damage: those observations enter the merge at full weight carrying
an intensity scale that is wrong by four orders of magnitude.
It surfaced when rotation started integrating every frame the sweep's lattice explains, but it is
not caused by that change - six crystals in the battery already tripped these guards before it. What
the extra frames did was find a crystal where the collapsed population is large enough to dominate:
R_meas 19.1 -> 90.1%, ISa 25.60 -> 4.58, from 17% more observations.
The frames are not sparse and the fit is not running away. A per-frame dump shows 3394 observations
on the median collapsed frame against 3469 on live ones - the scale is over-determined 3400:1 for
one parameter - and 113 frames fit exactly zero. They form one contiguous arc of about 68 degrees
once the sweep's wrap is accounted for, over which the per-frame correlation to the merge is 0.035
against 0.85 elsewhere, while the flux measured from the background varies by only 1.55x. So the
fitted zero is a well-determined measurement that the frame holds no diffraction from this lattice,
not a failure to measure. The frames are empty, not under-determined.
That is also why the smooth or shrunk alternatives do not apply, and both were built and measured
rather than argued away: giving a collapsed frame the geometric mean of its credible neighbours is
worse than the baseline (R_meas 115.3%), because it merges noise at the weight of a good frame, and
a dead region 112 and 232 frames wide has no local neighbourhood to borrow from in any case.
Dropping them: R_meas 90.1 -> 38.3%, low-resolution R_meas 26.9 -> 10.2% (past XDS's 14.3), ISa
4.58 -> 22.00, CC1/2 99.0 -> 99.9, with 5.4% more observations retained than before frames were
integrated at all. Over the full battery, against the same binary without either change, ISa moves
from -22.5 to -3.4 summed, CC1/2 +24.6, and 216247 more observations. The crystal that motivated the
integration change is untouched by this one, bit for bit.
The detection and the MIN_CREDIBLE_SCALE_RATIO threshold are unchanged. Note that threshold is now
marginal: its own comment records 0.070 as the smallest legitimate ratio seen, and one crystal here
has a legitimate live frame at 0.026, so it cannot be raised to catch the partly-dead transition
frames at the edges of an arc without risking real data.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 5
b9078d9a59