I make sure my servo arm and horn on the rudder are the same size - for example 3.00 inches. Now the cables have to be parallel and exactly 3.00 inches at the exit. I measure the width of the fuse with a caliper and find out where it is exactly 3.00 inches wide. Mark both sides with the edge of a piece of tape. Mark the height of the servo arm on the outside of the fuselage next to the rudder servo. Have someone hold a piece of string on the side of the fuse at this point and you hold the other end of the string on the rudder horn. Where this string intersects the piece of tape near the tail is the exit hole location.