Part of our De-Install process has been to zero (center) the iLIGO Scissors Tables to put the In-vacuum support structure at the nominal height ready for aLIGO.  One issue though is that there may be tolerance stack ups, as well as the weird V-Block Connection, that could put the Support Tubes/Support Table at non nominal Height.

We measured heights from the North HAM10 Piers to the HAM10 Support Table and from the HAM8 NW Pier to the top of the NW Support Tube end.

The shots on the HAM10 NW pier showed the Pier level +- 0.001"
The HAM10 NE pier was within .009" of the NW Pier.
The average elevation of the HAM10 Support Table was within .004" of nominal height.
The SE/NW axis of HAM10 Support Table was tilted about the SW/NE axis +-0.047".
We weren't able to shoot the HAM10 Support Tube Tops but we did that at HAM8

The HAM8 NW Support Tube was 0.065" higher than nominal relative to the NW Pier.

I think the takeaway here is albeit with a small data set, the Support Tables [& tubes therefore] will on average be at the correct height with respect to the Piers.  However, while zeroing the Scissors Table will put things at nominal average, the V-Block connection could give the out of level condition.  My recollection is that we want a much more level table than this.

I do think we can measure the situation on the outside with just pier to support tube observations.  I need to measure the HAM10 Support Tube to Pier to confirm.

Attached is Note Book page.