I tried searching through this thread and also used Google search in an attempt to find the answer to this question, but to no avail. If I missed it in this thread please forgive me.
There is a thread here on SB that derides the conservatism of Suunto computers and their implementation of the RGBM algorithm.
http://www.scubaboard.com/forums/computers-gauges-watches-analyzers/346506-suunto-really-bad.html Please enumerate all, if any, differences between the implementation in the Atomic Aquatics Cobalt vs the Suunto family of computers.
Thanks,
This is not a simple question to answer, so I'm going to use some simplifications and shortcuts to try to answer just the question I think you're asking, without opening a full theological discussion of deco algorithms.
RGBM and the earlier (but still used) VPM are "bubble" algorithms. They are based on the physics of bubble formation rather than the empirical testing of research subjects that forms the basis for most other algorithms.
RGBM as a marketing label refers to an algorithm that attempts to reduce bubble formation by limiting the bubble size, rather than reabsorbing bubbles that have already formed, and does so under license from Bruce Wienke, the developer of RGBM. How this gets accomplished, and how conservative the profiles are, can vary considerably from implementation to implementation. Saying a computer is RGBM has no inherent bearing on conservatism, excepting that RGBM will tend to emphasize slower ascents and deeper stops. In general, the Atomic implementation of RGBM is less conservative than Suunto, but we are not talking about huge differences. And it can be very difficult to determine what one means by "more conservative"- penalizing rapid ascents more? Lower NDL's? Shorter schedules when in deco? "Locking out" violations? It's actually pretty complex. We never lock a diver out, for instance- though we have VERY prominent warnings if a deco violation has occurred. NDL's are generally more liberal than Suunto- though I can't say that will be the case for every profile or dive series.
There is also a "full" RGBM algorithm that is referred to as "iterative"- which just means it does all the bubble calculations and comes up with a profile designed to keep bubbles under a certain size. This is done by modeling mathematically the known physics of bubble formation. The calculations are very computationally intensive have therefore been the province of very powerful computers or even supercomputers until recently.
What has generally been the case with "RGBM" computers is that they are actually running a conventional Haldane algorithm (which is computationally easier to implement) and adding "bubble factors" to come up with limits and profiles that match those calculated by the "full" RGBM calculations, and meet the particular conservatism level chosen by the manufacturer. This works well within normal limits of recreational exposure. That is what Suunto does, and that's what the Cobalt does- to a point.
At depths below 150' the Cobalt switches to a fully iterative RGBM implementation, using code we developed back in 2003 that enables the "full" RGBM algorithm to run efficiently enough on the Cobalt's microprocessor to be useable in a real time system- while still doing all the other things the computer needs to do. In a desktop dive planner the code must run only once for a profile- in a dive computer it needs to update constantly and provide live feedback to the diver- a much more difficult problem.
At this point running fully iterative bubble models in a dive computer (as opposed to desktop software) is rare- Liquivision has VPM-B software available as well as (I believe) a full RGBM implementation. I don't know of any others. As much more powerful processors are readily available for handheld devices, this path becomes an increasing possibility. In the Cobalt, however, fully iterative RGBM will only have an impact on deeper decompression dives.
If you go to the thread
http://www.scubaboard.com/forums/co...mic-aquatics-dive-computer-4.html#post5601716 in this forum section you will see a discussion at about post #90 that covers why this is the case.
Ron
That stuff is about as strong as you can get and its able to withstand salt water.
