elevator balance
Giffen A Marr makes some good analogies about a trailer and balancing of control surfaces. However he is wrong.(I think) we are flying in three dimensions and not driving a trailer. flutter is a very complex problem,I dont pretend to understand all of the possibilities however ive experienced it and worked on many projects with experts who do and(I think) the best way to balance control surfaces is 100%. if its nose heavy it can flutter and if its aft heavy it can flutter.(if its balanced 100% it can flutter also but less likely) hold a control surface at the hinge line  with something that will allow the surface to rotate and then move it upward very fast. If its balanced it will stay level. if its aft heavy the control surface will rotate on the hinge with the heavy side lagging the same holds true for nose heavy. now picture your wing flying into a gust, as it moves up the aileron stays level if balanced. if unbalanced it will move and depending on the stiffness of wing and a hundred other variables it may self excite.(flutter)
dave