We've been seeing the sqz angle needs adjusting between the start of the lock and a few hours in 68853.

This morning I tried to optimize the SQZ angle every ~10minutes after the start of the lock (IFO in NLN at 15:47 UTC). I aimed to reduce the 3,4,5,6 BLRMS, ADF RMS at 1300Hz and the DARM plot. See Operator's SQZ Troubleshooting Wiki for some SQZ angle tuning instructions. Results attached. The angle changes around 20 degrees in the first 1h30 of the lock. We could think about adding a SQZ angle adjuster to the THERMALIZING guardian or something similar alog#68948. However the optimum angle is tricky to choose as there's a fairly large (+/- 10deg) range that gives very similar squeezing, see attached plot taken at 17:30 - 17:40 UTC (1h40 after NLN). 

We could try to retake Sheila's pre-O3 squeezing verus angle  alog#55760 plot overnight in the next weeks to understand this better. 

Daniel suggests checking the stability of squeezing using the ADF calculated SQZ angle (H1:SQZ-ADF_OMC_TRANS_SQZ_ANG). See attached for how this increases 15deg in the first 1 hour of a lock. Nominally the ADF line is off and we don't yet have data for a clean long lock where the SQZ angle wasn't adjusted.