I detailed Fitts' Law not too long ago in one of my usability terms articles (the series will pick up later on, by the way, I am currently too busy with my bachelor's thesis), and this article is a very detailed addition. It is a little old (October 2007), though. "Back in school, I remember that it wasn't until I started taking classes in physics that calculus made any kind of real sense to me. I just need diagrams to function. In that spirit, I thought it would be nice to go over Fitts's Law, a staple in the HCI diet, with a few visuals to explain both the concept and why it's ideas are a bit more complicated than most would have you believe."