| Sorry for the delay Mark in replying, been busy with the kids.
A couple of points on what you have said above.
1. Ratio Deco works because, within a certain window of operation, a certain increase in bottom time, increases the deco obligation by the same amount. I ran through some examples last night using 45m (limit of DP qualification) and 25% & 50% alongside 21/35 & 50%, GF 30/85, to see what figures came out. You are correct that the times are very similar but if you the depths are changed the deco time changes are not quite linear (and neither are the standard gas deco times) but the way the times are spread/change would be harder to do from memory. As you increase times from 30mins to 50mins at 39m using 25% & 50%, the change becomes closer to 2:1 rather than 1:1 at 30mins whereas 21/35 and 50% still remains at 1:1.
2. I have not done enough investigation into the profiles to see what happens with regard to 'shaping a curve' on Nitrox mix but I would have thought that it would have been biased for a shallower deco profile making adjustments a little harder to do from memory. This would be especially true if diving a nitrox mix rather than trimix. Diving Nitrox to 40m+ in the UK is something which you (and quite a few people on here) agree is not a good idea.
3. When I talked about 'skillset' I meant the knowledge to go into Deco programmes and play with multiple profiles to spot the patterns which make up the basis for RD. You are correct, and many people have agreed, you can create a RD profile for any gas set but it does take time and you need to go through lots of profiles to see what the patterns are. The RD patterns from AG and GUE have had alot of scrutiny and people who use them know what the limits are and know how they can 'frig' the figures to take into account the agressive side of the scale. Creating your own RD profiles isn't an easy task. However, if you want to cut tables for longer, deeper, longer & deeper you will see what can be acheived. As long as you use the same gas each time, those tables are re-usable as Paul said.
As I said before, the best bet would be to go on the course, use tables and a timer (as that is most likely what will be taught), talk through with the instructor what gas computer options are available with their respective pros and cons and go from there.
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Team Foxturd Son, you're going to have to make up your mind about growing up and becoming aircrew. You can't do both.
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