chrisch once bubbled...
I did however find an old BBS posting by Bruce that gives some better background. It is hard going, so I guess I need to buy the book..
I can see that an ability to figure out a deco when things go wrong would be a very useful thing. I don't now think that's what I am going to find. Thanks to everyone for the links though it has been interesting reading.
Chris.

As for your second comment, I would like to re-inforce that by saying that it is not just useful, but absolutely essential. With a bottom timer, and waterproof tables in your pocket, you have a solid back-up to your wet computer.
....And, lest anyone should call this heresy coming from me, I have always said that Mr. Murphy lurks near-by at all times. It is extremely prudent to have back-ups!
Remember: CDRYB/LOUD =-)