Sillyness posted this a while ago in the GS forum:

Set your ATVs to approx 130% up and down (130% is for JR... may need to use slightly less on Futaba or Multiplex) to allow room for subtrim. Then I roughly center the surface with subtrim. Measure up and down throw. If you have more up than down, then shorten the pushrod (and vise versa). Now, re-center the surface with subtrim, but do not touch the ATVs... leave them alone at 130ish%!!! Re-measure up and down throw and repeat the above proccess until the surface moves the same amount up and down. Your servo arms will likely be tipped slightly toward the rear when done, but it depends on your geometry. If you end up using excessive subtrim you may need to rotate the servo arm 1 spline one way or the other. Look at your servo monitor page to make sure you aren't over-driving a servo (i.e. a servo stops before the stick reaches full travel). To get more travel both ways after they are matched (up & down) you need to move the clevis height on the control surface

The result is a setup where both halves will travel at exactly the same speed and they'll track together perfectly throughout the range of motion.... very linear. To get more travel both ways after they are matched (up & down) you need to move the clevis height on the control surface


It might take you 30 minutes to do the first one, but after you learn how to do it the second one is a piece of cake.