Jim:

The exactness of the CG setting is really of no consequence so long as it is within the flyable limits of the CG range; that's why the fingertip method works fine.
The pilot of a General Aviation airplane or a Jet Transport (and some RC pilots too) could care less who or how many people get aboard (which causes a change in the exact location of the CG) so long as you're within the flyable CG range.
I use math in the design phase to eliminate the need for unwanted ballast.

feihu