Square root of a negative number...? Oh, I just got it. He's saying the numbers are imaginary.
And I think the Mobius strip is a good analogy for Dilbert's work timeline. PHB tells him what problems to fix, he fixes them, and before he knows it the PHB is asking him to fix problems again.
This is probably the funniest Dilbert I ever read. When I read it in 1999, I clipped it and kept it on my dorm room door, when everyone else could laugh and enjoy it. Over the years, I have found this strip (usually when I'm moving or doing major house cleaning) and I read it and keep it again to get a very good laugh for the next time I come across it. Now with the online feature, I have it here as well.