A fixed-chi stage carries phi at a standing angle to the base circle, and states
that angle in the CBF _axis table and nowhere else - its "# Chi" line reads
0.0000, because no chi circle is driven. ParseAxisTable kept only rotation axes
hanging off nothing, so the inclination was discarded and RotationAxis() fell
back to that zero: a phi scan was run about the base axis, tens of degrees from
the one the crystal actually turned about.
Measured on a magic-angle head 54.74 degrees off omega: the axis goes from
1 0 0 to 0.577382 -0.707087 -0.408237, against dxtbx's 0.5774 -0.7071 -0.4083,
and the first pass from a P-centred triclinic 27.2 58.1 126.2 that indexes
nothing to P-orthorhombic 5.16 14.05 14.81, which is the cell DIALS and XDS both
reach on these frames. The mirrored inclination returns to nothing, so it is that
angle and not any perturbation of the axis.
Every other header in the corpus states one rotation axis, which is every
Eulerian head, and is untouched. The two that share this table were written three
days later by a template that puts the same angle on the "# Chi" line, agreeing
to 0.03 degrees - they read identically either way.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011GxZqDiFP3KqriBhNdcR56
leonarski_fandClaude Opus 5
e3da313c84