Originally Posted by Towlie
Well, I'm thinking it's the axis of rotation in question here, which is central to the head tube, and to the fork as well since the fork is mounted to the head tube.
If that was the case, wouldn't it be easier to say your upper arm should line up with the head tube? This sounds like the whole KOPS theory. Someone noticed that alot of people are setup this way and figured that is the correct way to do it without any scientific evidence to support it. See Keith Bontrager's article on the myth of KOPS
http://www.sheldonbrown.com/kops.html