My book says 3.25 - 3.5 in. from the leading edge, at the fuselage sides. I am right at the 3.5" mark, and mine, to me, seems nose heavy still. Here is my CG Machine. If you use new pencils, the erasers cushion the point of impact just right. This probably would have to be modified for heavier planes, but works well up to 60 size anyway. I use about 1 - 1.5" of masking tape on the wing where I mark the forward, center, and aft of the cg, this way when I am done with it, I don't have to erase ink or marker from the wing.