Funny you should ask this!
I've recently been looking at Nitrox tables to refresh my knowledge (course done years ago) in doing so I have produced a set of Nitrox tables that are remarkabley similar to the PADI ones.
I did work these out from formula and have put them on this web page
http://www.scubadivingtours.co.uk/nitrox/
I still need to put the formula on each page so people can check for themselves.
I could also do a set for air.
Anybody got any formula that calculate maximum dive time and pressure groups, and I would be interested in formula for surface interval and reduction in pressure groups also.
Any help
Jason