You all are making it too complicate! What I have done over the years is first get the rods set in the approximate position with them attached to the elevator servo which is in the neutral position. Then set one elevator half to neutral by screwing in/out its clevis. Then set the other half by again screwing the clevis in/out eyeballing the position of the two elevators from 3/4 feet back of the rear of the plane. You will find that the result is quite accurate.

Bruce