Not really a formula is it, just a table that says if CSS is 2 below par then you need to be +2 to play to your handicap
I'm not convinced that works - For example a player (18hcp for arguments sake) could walk off the 18th green with 38 stableford points but because he'd had 2 nett eagles 3 nett birdies and 5 nett single bogeys he's finished the bogey comp at 0, so assuming par=css on the course played he wouldn't get a cut.
