Oh Marv..... that raises a WHOLE NEW conglomeration of issues. Imagine the government using a pan of Mercury as a reference for level. The EPA would have to get involved, there would be men in hazmat suits, with respirators. Yellow tape strung up all over. They would double bag Ralph's cell phone so they can haul it to an EPA approved Hazardous Waste Disposal Site. ......
Seriously though. This was a very enlightening project for me. It is fascinating to have an instrument as sensitive as this one is. After calibrating my new level, I set up my 6 foot, aluminum bean level on my bench. I used shims under each end until it was "level" then placed this new level on top only to have the bubble almost pegged against one side. Thinking that surely I must have messed up the calibration of my new level, I turned it 180º and had the same reading. Being about 3 graduations from center, each graduation represents .005 per foot. 3 x .005 = .015, my level is 6 feet, 6 x .015 = .090. Putting .090 shim under the low end brought my new level into the center, and barely moved the bubble on my carpenters level
I was able to tweak a bit of twist from my lathe bed already. I have to wait a few days to see how things settle since I made those adjustments.