Purchasing your first dive computer. A non-technical approach.
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I think the OP is right that there can be a benefit to simplifying the process of choosing a first dive computer. When I started diving, two friends who have been diving for decades advised me. They said which algorithm they prefer and why, which brand and why, and suggested that I buy that brand's least complicated and least expensive model. It was good advice. It sounds like the OP got similar advice from the LDS. And, yes, I've read and re-read the manual.
I'm sure you realize this spawned from amentionbashing of suunto whose programming is allegedly based on a bubble formation model. You must have heard that one of its "features" is better off-gassing at deeper stops.
I'm unclear on the point you are trying to make.
Someone said that you would off-gas more in 3 minutes on the surface than 3 minutes at 15'.
Someone else asserted that that is not true. My post was making the point that it IS true - unless you're breathing something like EAN50 or even richer. No more, no less.
My comment was that bubble theories imply that it's only true if bubble size doesn't go over critical radius. If pressure difference from max. depth to surface is large enough to push it over critical radius, and pressure difference from max. depth to safety stop is not large enough to do that, then a bubble model will have you off-gas more in 3 minutes at 15' than in 3 minutes on the surface. If that is factored in in Suunto's programming, then it should "reward" you for longer safety stops over longer surface intervals. In which case the claim that it won't penalize you for skipped safety stop is only true for some values of "penalize".
The quoted manual implies that they base their critical radius guestimate on the ascent rate more than on pressure differential, but obviously, who knows WTH it really does. Whoever cares needs to buy an OSTC and read the source: it's the only way to be sure.
I think you're mixing together the chance of getting DCS and the amount of off-gassing, which I'm not sure is correct in a bubble model. You could be off-gassing the same amount and still have bubbles get big enough to cause DCS. Regardless, I was talking about actual off-gassing, not what Suunto's model says.
Also, apparently HW is no longer open sourcing their computers. So, if you're talking about an OSTC 3 or 4, you can't be sure with them, either, I don't think.
Ah. I was stuck in the Suunto tangent, and no: it is talking bubble size as in small enough to get through cellular membranes. If they are, they'd come right out in the lungs, if they aren't: you have to wait for them to get re-absorbed before they can come out. Hence less efficient off-gassing when bubbles are too large -- not the "big enough to cause DCS" too large.
Of course other experts say no bubbles can pass though cell walls and therefore all bubbles are too large to off-gas efficiently so... deco theories are like standards: we got plenty to choose from.
Bummer. Did they change the name to CSTC as well? Or DFKAOSTC (Device Formerly Known As)?
There was test done several years ago comparing many different dive computer algorithms. The computers were all strapped to a tube and taken to depth. I believe 4 consecutive dives were done with surface intervals and profiles similar to typical recreational dives. The article was pretty detailed and showed a big variation in conservatism, especially for dives 3 and 4. Suunto was one of the most conservative, but there were others.
The latest high end Suunto computers may have a different algorithm or allow adjusting to be more liberal, but I believe the Cobra, Gekko, Vyper, Zoop still use the same old algorithm. Good computers for conservative recreational diving, but worth comparing the algorithm to what you currently use to see if you will notice a difference.
I like liveaboards doing 3- 5 dives a day or Cozumel 2 dives a day 75+ minute bottom times, both on nitrox. I liked my Suunto Cobra and dove it for many years, but decided I wanted something that let me adjust more liberal.
The latest high end Suunto computers may have a different algorithm or allow adjusting to be more liberal, but I believe the Cobra, Gekko, Vyper, Zoop still use the same old algorithm. Good computers for conservative recreational diving, but worth comparing the algorithm to what you currently use to see if you will notice a difference.
I like liveaboards doing 3- 5 dives a day or Cozumel 2 dives a day 75+ minute bottom times, both on nitrox. I liked my Suunto Cobra and dove it for many years, but decided I wanted something that let me adjust more liberal.
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No, but you can question which laws of physics apply to a complicated biological system.
I am not sure where I read it but I am pretty sure I have seen it claimed that once the bubbles get going they prevent proper blood flow such that off gassing is reduced. If that is the case then you would be better deeper. That might only happen once you are getting bent, but, if true, it isn't universally the case that shallower will improve offgassing.
Porridge may be too hot, too cold or just right.
I think it's about what one's made of. I, for example, have a large organ between my ears that I value a lot. I believe it to be largely fluid and fat-like tissue, both rather sensitive to decompression issues. I therefore choose to use a more conservative computer for extra protection up there. If, OTOH, the tissue in question is mostly bone, one should be perfectly OK with a more liberal approach. Like DSAT, or GF99/99.
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