ORIGINAL: bubbagates

Now program the servo to get the same amount of arm movements in both directions, let's say 50 degree just for an example

Now connect you linkage and with everything on, adjust the control horn and control rod to get the surface centered. Now move the stick in one direction and take the measurement in either inches/MM or degrees, I find millimeters to much more accurate for this. Now move the stick the other way and take the same measurement at the exact same spot. If the control horn is installed correctly and the geometery is correct and the control rods are exactly the same length and the arms are long enough, you should be very close if not right on with getting the same throw in both directions and as much throw as you are looking to get. Lets assume you are getting the exact same throw for now and the amount you want.