OK----Another low-tech method.....
Pin/tape long balsa sticks along the centreline of each stab tip(or along the elevator tips with these tips aligned with the stab halves, depending on the design)
The sticks must project behind the rudder.
Now stand well back to one side, and the sticks should be parallel to each other.
You can use the same method to check wing tip alignment.

Now ask what to do if the tips are curved in plan view!?