I linked to this along time ago from my site, I thought you guys may like it here as well. very informative in a maddening, hair pulling, teeth gnashing sort of way. Spreadsheet is available for download from the site as well.
"The principle PR problem with the various BCS computer ratings (Sagarin, Massey, et al) is that the average fan has no idea where they spring from, let alone what's happening inside the various black boxes. The truth is that they really aren't that complicated. The rest of this post is my attempt to pull back the curtain on the how most BCS computer ratings are estimated for the casual fan. Don't fret, only a very modest amount of math is necessary. The rest of this post illustrates -- step by step -- how you can faithfully recreate the current BCS ratings via a downloadable Excel spreadsheet. I'll start with a simple intuitive example, then apply it to NCAA Division I-A games through October 31. Consider this your own free personal BCS computer.
Got the curiosity and a half hour? Let's go."