Lowering a beetle

I want to lower my beetle about 2.5 in by adjusting it a few splines on the rear, is there a standard eg, 1 spline = 1 inch?

How many splines should I adjust it, or is it all trial and error?

Thanx in advance

Here you go

http://forums.aussieveedubbers.com/viewtopic.php?tid=78303

How coincidental, I just got my Oval on the road with a IRS backend and I set it to low when I put it all together, rides well but doesn't like bumps. I was reading this morning on how to change the ride height. Great article well done. I will put it into practice tomorrow
Cheers