Thanks Johng,
That explains why the plane should be level when using this tool. Would you say that this method is more accurate than the Teeter Totter tools since there is some friction in the rotating parts of the those tools. I think for our purposes, somewhere within 1/8 of an inch is probably satisfactory unless you are balancing a model like the Stealth Fighter (I hear you got to be right on the money with that plane).