During the second UVa cooldown spectral data were acquired for different rotational orientations of the dewar in 45 degree steps. The electronics cabling at the time prevented complete rotation of the dewar, so the dewar was first rotated 135 degrees CW then back through zero to 135 degrees CCW in 45 degree increments. Frames were acquired at every 45 degree step along the way to check for hyseresis as well.
The figure below animates the motion of the spectrum through all 13 positions of the instrument. Based on centroids of the individual dots produced by the spectral comb the maximum observed excursion is 0.9 pixels in the spectral directon with virtually no observable motion along the slit direction. The is no evidence for any significant rotational component 0.05 pixel level from the top to the bottom of the slit.
The sequence began, passed through, and ended at zero rotation (necks up). The animation of those three frames below shows that the flexure does suffer from hysteresis at about the 0.5 pixel level.