None.
The base timing value in the handheld can be used to help adjust phasing some. Tough to explain, but that value adjusts the rotor relationship to the terminals to some extent. I haven't needed to do that yet though.
I put a hole in a spare cap and checked it, and found it to be pretty darn good. I run with a 15deg base timing, 22-24 initial, 34 total and 50 at low map cruise.
