If you have a combination sqaure laying around, this is ideal for marking the Cg on your wing. If you don't, a cheap one is only $5 at Wal-mart. Just set the square at your desired point and lay the ruler part on the wing bottom while pressing the short part against the leading edge, requires you to tilt the ruler on edge a little, and then you just mark the wing along the end of the ruler. BTW a slightly repeat slightly tail heavy plane will take off quicker and land a little slower and easier than a nose heavy plane. This is how I set up my trainers, just my preference though.