Just out of curiosity, where do the figures come from for rear beams?? I.E on Mike Rainbirds ultimate spec saff, he quotes it as having a 6 degree rear beam, where is this measurement taken from? Is it the amount of adjustment it offers, or is it the angle at which it is mounted to the car?

I need a rear beam sometime in the future, just wondering what options are out there at the moment, I take it Zoo beams are no longer availiable?