Yeah, that link had a stack of info, exactly what I was after thanks. The toothpick method is good, but they reckon the straight edge method is better. Hope I'm allowed to copy and paste?

"Unfortunately the toothpick alignment is really not the proper way to align a flipper. Instead take a straight edge and use the lane guides to give the flipper bats a final position adjustment. The ball should roll off the guides and to the flipper bat in a straight line, which should be easy to see with the straight edge."