What works for me:
70 and 80 feet air NDLs add up to 110, and you lose 5 minutes every 10 feet beyond there, and 60 is 55:
60 - 55
70 - 40
80 - 30
90 - 25
100 - 20
110 - 15
120 - 10
130 - 5
For EAN32, use depth - 20.
For the deep portion of the dive, if its a reverse profile, take the max depth. If its not, then use avg depth. For multilevel diving with an 80-120 portion of the dive followed by a 60 foot level, take twice the time deep and add to the time at 60 and apply to the 60 fsw table value (only really much of an issue with air).
Once you start talking about air at <=50 fsw or nitrox at <=70 fsw I need to get out because I get cold.
Ideally I do 1 min 'stops' all the way up. Minmum is doing 1 mins from 1/2 max depth. For repetetive diving extend the shallow stops to include at least 2-2-2 to the surface. Typically do more like 1-1-1-3-3 and spend some time working on trim, hovering, clipping and unclipping and whatnot shallow. For real underwear soiling emergencies, skip the deep stops and do 1-1-1 and get out, extend 10 fsw stop if there's time. Add more time shallow arbitrarily for cutting it close to the NDLs and/or repetetive diving.
Do at least an hour for an SI, longer if repetetive diving (n>=3) and/or extend shallow stops.
And some bright scholar will probably find some edge case where this doesn't work at all, so don't do that. The wider the discrepancies from a square profile, the more none of it applies.
And usually it is much simpler than this. The dive plan is usually "lets go down to 100 fsw for 30 mins on EAN32" and then you adjust from there based on how much you overshoot or undershoot it, which is usually +/- 10 fsw. And usually on a dive like that I'll scoot up from 90/100/110 fsw up to 50/60 fsw or shallower which will effectively give an NDL longer than I care to do a dive (on EAN32) -- the faster compartments which had been your controlling compartments have their clock stopped at that depth and the compartments you're loading are pretty slow.
I'm also very comfortable with managing a gas plan in addition to this, and drill a lot on solving problems at depth, so I'm comfortable with the idea that I may have an actual, although small, decompression obligation per tables and when there's doubt I extend the 10-20 fsw time. I also know, on the fly, how much psi to add to my rock bottom to deco me and buddy at 10-20 fsw very conservatively.
I've also run my computer in parallel with my brain in trying to figure out a lot of this, and I get very good agreement.. I've pushed a minute or two into deco on a couple of occasions per the computer, which all cleared before I even ascended above 40 fsw, and the most I've gone over has been 5 mins of obligation (and that's on a conservative suunto computer). Plus, I frequently forget to set my computer to EAN32, and it goes 10-15 mins or so into deco and I get in good practice at dealing with simulated deco obligations...
