Alternate Static
I had better dive into the books to confirm this but I think you will find that the Bandit has two diferent tailplanes fitted depending on the model..One has Zerro angle and the other 7 degrees. The wings on all models are 10 degrees. As someone mentioned earlier the tail plane diheadral is to reduce the effect of vibration.
This is the best forum on pprune..at least here we can actually learn from each other and just think of the enormous knowledge bank we have access to.