In order to address the issue of low MC1 OSEM voltages, Yuta and I looked at the IMC table levelling. Looking with the bubble level, Yuta confirmed that the table was indeed out of level in the direction that would cause MC1 to move closer to it's cage, and therefore lower it's OSEM voltages. Looking at the trends, it looks like the table was not well levelled after TT1 installation. We should have been more careful, and we should have looked at the MC1/3 voltages after levelling.
Yuta moved weights around on the table to recover level with the bubble level. Unfortunately this did not bring us back to good MC1 voltages. We speculate that the table was maybe not perfectly level to begin with. We decided to try to recover the MC1 OSEM voltages, rather than go solely with the bubble level, since we believe that the MC suspensions should be a good reference. Yuta then moved weights around until we got the MC1/3 voltages back into an acceptable range. The voltages are still not perfect, but I believe that they're acceptable.
The result is that, according to the bubble level, the IMC table is low towards MC2. We are measuring spot positions now. If the spot positions look ok, then I think we can live with this amount of skew. Otherwise, we'll have to physically adjust the MC1 OSEMS.