Assuming you're using something like HS75's or RT88's as the servo's, there's no adjustment: they turn 180*. You put the servo arm/pushrod connection mechanism on each retract, then adjust the servo arm/pushrod to produce the required amount of travel to activate and lock the retract in the up/down position. Then you plug each servo into the end of a "Y" connector, and the other end of the "Y" into your retract channel. Each servo will rotate the same direction, so the only thing you really need to check before tightening up all the screws is that each both retracts are opening/closing when activated. If one is going the "wrong" direction, move it's connection to the other side of the servo arm.