I do, not really handy in internet form though. Basically it goes through a long, dry explanation of;
'if target is crossing at 100 mph, put target on the ring'
'if target is crossing at 50 mph, put target halfway to the ring'
and so on.
Obviously the question pops up as to how the heck the pilot is supposed to know the crossing speed of enemy aircraft. Apparently the RAF (eventually) thought the same way and trained their pilots in a more fluid, 'gut feeling' manner, as seen in 'Bag the Hun'.