I got the diagram from seymour duncan's website. It said you can split it for a non-adjustable inner coil, or an adjustable outer coil.
Whats the difference and which is better?
as far as I know it's so that when you have two humbuckers split and on at the same time, it acts like a 3-single coil guitar in switch positions 2 or 4 (so it's hum-cancelling)