At the moment I'm wondering who this machine is aimed at. The majority of divers that use it wont be doing sub 40mt dives. So they'll be using an algo that is something like that found in the Suunto & Mares RGBM computers. Personally, I don't want to go back to something that will penalise me excessively because I'v gone on a 7 day live aboard & do several dives every day. If I didn't know something about the algo, I may have found myself with a machine I had little use for.
OK, back home now so I can address some questions.
This computer is aimed primarily at a recreational user, most of whom will not dive anywhere near its capabilities. Obviously, we are planning other products down the road that could address other groups of divers.
I think you can lay your concerns at rest. The "folded" RGBM used at depths less than 46m/ 150' is just a method of calculating a diver's decompression status, and does not in itself imply any particular level of conservatism. The Cobalt's implementation is in fact much less conservative than the Suunto implementation (as our field testers discovered), though the underlying methodology is essentially similar- as it is in all Haldane/ Buhlmann computers. Details of the implementations, such as the chosen M-values and the penalties given for repetitive, deeper than previous, or multi-day diving, etc., result in variations in conservatism. The same is true for full RGBM- there are software "handles" that can be used to adjust baseline conservatism. Cobalt has a built in simulator, so you can easily check to see exactly what NDL's or deco schedules a particular set of repetitive dives will generate.
I find it interesting that a fully iterative RGBM algo doesn't scale from NDL to deco. I can't even imagine why anyone would shoehorn the full RGBM into a recreational machine & then only use it sub 45mt. I have to admit it makes me think cynical thoughts about marketing departments.
What happens if I do a 35mt dive for 30min? Am I using a full RGBM, or a hacked, single phase model? Why does BRW recommend the hacked single phase model for "shallow dives & light deco"? Is there some problem with the basic tenants of RGBM that prevent it from scaling between deep & shallow, long & short dives?
I can tell you this was absolutely not a marketing decision- on the contrary, from a marketing perspective, just saying "full RGBM" would have been much easier.
BW, who provided the algorithm specifications, maintained quite strenuously that "full" RGBM was not necessary and should not be used at shallow depths. This I am sure comes from real world validation as well as from theory. It does not imply any problem with the basic tenants of the model, just that it has areas where it operates more efficiently. One way to conceptualize it might be that at deep depths the bubble factors dominate in arriving at an efficient staging regime, and RGBM is designed to calculate these schedules. At shallow depths/ shorter exposures the saturation considerations are more often limiting factors, and the older tried and true models are more efficient in arriving at a safe schedule- though factors are added that take bubbles into consideration. That's the "folded" part. The folded version, which is what would be used at 35m, is "hacked" only in the sense that it has added components that model some of what we know goes on with bubbles. It would probably be be mathematically possible to tweak full RGBM to give close results by increasing the conservatism as depths are shallower, but it wouldn't make much design sense to tweak a computationally intensive model to mimic a much simpler one. Given much more computing (and battery) power, we could run both models side by side and chose the limiting factor. The bottom line is the schedules being efficient, accurate, and safe, whatever the method.
I hope this clarifies more than it confuses the issue.
