This cannot detect the exact nav roll position. It just detects if the designated part is too low or too high or too far sideways to either side.
How it works:
1. Make at least a 4x symmetry
2. Break Symmetry
3. Name all of the parts differently so that there are no duplicate part names. You can do this with things such as Fin 1 and Fin 2.
4. Modufy the program to set the parts accordingly. Make sure when you name the parts you do them in order. If you want the one on top to be East (what the program is set to) then make sure that the variable F1 is set to the position of that part. Then make sure that the one to the North (indicated by the blue arrow in the designer) is F2. If you have multiple North fins like the rocket I am designing; then set the one closest to F1 to F2 and the furthest one to F3. You do not need to set every single Variable.
5. This only works for East bound rockets. It does not have to be true.
@Tweedle_Aerospace thanks this is really helpful.