Alena Anayeva has been working on some zeemax modeling to help us understand what happened when our output arm seems to have changed on April 22/23rd. 

She has been using shifts in alignment based on slider numbers as reported in 77388, but the shifts that this is giving her are too large. 

This is a quick look at the slider calibrations.  There is a discrepancy for SR2, the slider calibration agrees with the M2+M3 osems, M1 osems are reporting a 62% smaller shift. For SR3, the sliders and osems agree to within 10%.

After the large shift we have been falling off the SR3 optical lever, so that is not a useful comparison.