Okay, a real quick note here...
In my experience, DIR-F did not teach deco theory. (My experience was the same as O-ring's.) Furthermore, I am not qualified to talk about deco theory. I am not yet a deco diver, and all that I know about the subject is what I've learned on my own accord by going and seeking the information myself. Until I receive that training, though, I refuse to dive with a deco obligation.
What I do know, and have resisted sharing, is the simple technique to calculate your No Decompression Limit "on the fly." Since most manufacturers of computers (even those capable of calculating deco) recommend staying within NDL's, then it hardly seems money well-spent to purchase a computer designed mostly to simply keep you out of a mandatory deco obligation... When that's simple to calculate "on the fly" by yourself, even on a multilevel dive.
I'm not sure how it came to be the opinion of the board here that I am not sharing deco theory. Perhaps I led y'all to believe that. That is not what I meant at all.
What I don't feel comfortable sharing is the "on the fly" method of calculating your NDL... In effect, having a table permenantly embedded in your brain, such that a computer seems pointless.
And it's not that you need "the secret handshake," it's that the system involves more than the simple knowlege of the math. It involves a whole mindset change, and substantial changes in dive style (or even lifestyle). And those things can't be taught over the Internet. They have to be taught with practice.
That's why I recommend that people take the DIR-F course if they want to know the procedure. It's no big magic... Just a simple rule that gets you a fair degree of accuracy with some math simple enough to do in your head.