During Maintenance March 15th, IM1, IM2, IM3 and IM4 all shifted alignment for the same given alignment drive.  The first shift was identified and restored, but the next two shifts were not, and IM2 pitch, H1's biggest shifter, jumped about 40urad in the same direction, so a total of about 80urad alignment shift in pitch.

I restored the alignments (including IM4) to the values before the alignment shifts March 15th.  I did so by moving each optic and leaving some time between each, so I could get a reading of how much each optic (IM1-3) changed IM4 Trans QPD.

The results are that IM4 Trans QPD is:

• 6x more sensitive to IM1 p than IM3 p
• 2x more sensitive to IM2 p than IM3 p
• 10x more sensitive to IM1 yaw than IM3 yaw
• 4x more sensitive to IM2 yaw than IM3 yaw

This suggests that the tolerance for alignment shifts on IM1 need to be smaller than the tolerances we use for IM3.  

Currently we're using a tolerance of 5urad on all IMs, and I would suggest tightening that up for IM1 to 1urad tolerance for both pitch and yaw.