Looking for a Site That Explains Pinion/Driveshaft Angles

I'm looking for a website that explains, mathmatically, the proper pinion and driveshaft angles needed on a 2-piece driveshaft. I remember finding one a few years ago and I think it was referred off this forum. Thx

I found a link to the site, but it appears to have been closed down. Bummer.

http://www.airridetalk.com/articles/drivetrain/the-u-joint-enigma.html