The theory is that 100% humcancelling is achieved by identical windings on each coil however the practice is that an offset between the windings of each coil allows more high end through. Different coil offsets effect the tone in uniques ways and you'd be surprised how much you can offset before noise is audible.To start with I wouldn't offset more than a few hundred turns.
The earliest PAF humbuckers all had offset coils, in fact the closest the cam to symmetry was within 100 turns of each other although most were at least 300 turns out.
Symmetrical vs asymmetrical coils is a raging debate. I strongly believe that offset coils sound head and shoulders better than symmetrically wound coils in the majority of applications.As always though, experiment!
