I found an error in that tut, in Demystifying the Greats 1
"

Now here's a sphere with a light shining on it. You can instantly tell there's light shining on the top right of it because that side is lighter, and the other side is of course, darker. It FEELS 3d, even though it's still just pixels like anything else we've been looking at...."
While it says top right I can clearly see top left. Not much of a problem but hey, I'm just pointing it out.