Several times over O3 operators have made note that they see SDF diffs for H1:IMC-MCL_FM_TRIG_THRESH_ON and H1:IMC-MCL_FM_TRIG_THRESH_OFF, and sometimes these are the only differences that prevent us from immediately going into Observe.  But, it doesn't happen all the time, which has made it somewhat confusing to track down.

I think I've finally grok-ed what is going on.  These thresholds are set in the IMC_LOCK DOWN state.  For cases where the IMC goes through its DOWN state while we're still ramping down in power after a full IFO lockloss, the DOWN state would set those thresholds assuming that we wanted to try to acquire lock at high power.  If the IMC caught lock, and then stayed locked until we next arrived at NLN, we would see an SDF diff.  However, if we ever lost the IMC and it had to run through its DOWN state again once we were already at 2W, then it would set the thresholds as if we wanted to reacquire at 2W. 

But, we seem to not have needed the filter that is triggered, regardless of input PSL power, for several months.  (The filter exists, and used to be triggered, to help the IMC relock.)  So, since it seems that we are doing fine without this filter, and anyway we nearly always reacquire IMC lock at 2W, I have just set these threshold values to be the 2W values, no matter the PSL input power.  This should prevent these from showing up as SDF diffs anymore.

Note that this reload of IMC_LOCK is the first one since June 4th, so IMC_LOCK only knew about the lscparams file as of June 4th.  Sheila and Keita did a lot of sleuthing (Keita is writing an alog), but it seems that the IMC_LOCK guardian thought that our final PSL power was still 35W since we hadn't reloaded the IMC guardian in so long.  See Keita's alog about his and Sheila's investigations for more details.