Stick your fingers under the wing @ 1/3-1/4 chord, if it doesn't balance there, you've got to move something! Calculating sounds like math and I've never considered RC as something I want to do math in, except to figure how what my wing/power-loading is. I fly "real" airplanes so I know how to do weights and balances computations but one can't exactly jack a "real" plane up at the desired "finger point" to make sure it's not tail-heavy...with most RC aircraft, you can!

KISS