I don't use anything. I set them the way I want them and eyeball them. I don't use the factory settings because it isn't enough. I set them to what I feel like. If I want to see if they match, I eyeball them there too, or use a ruler. Just another tool in a drawer that you don't use after the first time you use it and realize it isn't needed. If you need another way, run the ailerons to full, use a piece of clear plastic, mark the trailing edge of the wing and the trailing edge of the aileron or flap, move it to the other side and see if it matches. Otherwise a protractor works, or a compass to measure distance, or whatever else you have laying on the bench or in the drawer.