samhill wrote:For our needs I would think you would still need a Dwyer or some other to have a known level to compare to just to make sure.
Not if your vertical scale is drawn out accurately and with demarcation lines scaled in 10th's of an inch, and you use a unity oil. It will read accurately in 10th's of an inch of water column. The tricky part comes only if you use an oil that does not have a density of 1.00 (such as Dwyer Red Oil).
One thing I might consider would be to tilt it a bit more steeply so the precision in reading it is a bit higher.