A calibrated eyeball I just get as much throw as I can, or estimate 45* for test flights. On the ailerons, I make a bluecor template of the aileron with less throw, then limit the other one to that much throw so I don't have any differential.
What Dan said. Think of it as clock hands. If the wing (big hand) is on the 9 and the aileron (little hand) moves between 1 and 5, you've got about enough for 3d!
For more subtle measurements (i.e. 1/8" evelator for an F5B model) I use a ruler.
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I just get as much throw as I can, or estimate 45* for test flights. On the ailerons, I make a bluecor template of the aileron with less throw, then limit the other one to that much throw so I don't have any differential.
