Ah, wait, sorry. When you hay half a step, do you mean a semitone, or half a semitone.
I think I may have just messed you around.
If you want it to read as Ab, then you can just use the tuner to read one semitone flat, or set the base frequency A to Ab which is 415.305
really sorry if I misunderstood and confused
Edit: yeah Ab1 =103.82625
Doh, sorry