I want my quarter back!

Factual Questions
1

Could somebody explain the formula used for determining the NFL Passer rating? The number 102.3 means absolutely nothing to me.

2

Here you go, have fun.

http://www.nfl.com/news/981202qbrate.html

Anything over 100 is good.

3

I should say that over 100 is exceptional, not just good.