I have always taken into consideration what the plans and manual show for the center of gravity... although, I feel that any time I check the balance on a straight wing aircraft, the balance point should be on the main spar of the wing(the thickest part of the airfoil). If the balance is set there, you should just need to trim the plane out. make sure that the plane is ready to fly when you balance it... i.e. battery installed, all radio equipment mounted and not allowed to move and you should be ok.