They won't be exactly the same due to differences in sampling & recalculation intervals as well as precision and round-offs. E.g. if one recalculates every 20 seconds and another: every 15 seconds, they can only "exactly match" once a minute (assuming their clocks are perfectly synchronized). That would be more pronounced during depth changes and should start converging once you level off.
Dive Computer No Deco Computations Question
- Thread starter butterwm
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They won't be exactly the same due to differences in sampling & recalculation intervals as well as precision and round-offs. E.g. if one recalculates every 20 seconds and another: every 15 seconds, they can only "exactly match" once a minute (assuming their clocks are perfectly synchronized). That would be more pronounced during depth changes and should start converging once you level off.
That has not been my experience. About a decade ago, I got a Suunto DX for testing and also had a Oceanic Atom I was using.
I was on a deco dive and the Suunto had me doing a lot of deeper stops which I was obeying. At one of the stops, I could see my richer deco gas that I had stashed about 3 feet shallower and my Oceanic didn't have me requiring a stop at my current depth so I figured I would get to the gas and accelerate my deco.
The Suunto had about a minute left at the current stop I was at so I just went to the gas.
That was a mistake. The Suunto went into violation mode (under water on a dive no less) and no longer gave me any stop information. It was insane. I luckily had my Oceanic with me.
I personally only dive Shearwater at this point. For the diving I do, I really don't think any of the other mainstream dive computers are suitable for me.
I understand that a lot of computers go into a 24 or 48 hour lockdown after surfacing and after a violation. I won't argue if that is right or wrong (but I do dive Shearwater computers which don't do that).
However, to go into lockout mode while on a deco dive is absolutely unacceptable IMO. Go ahead and penalize me or alert me or whatever, but to lock me out during a dive is ludicrous.
I will never dive a Suunto again.
- brett
David Carron
Registered
I've given a fair bit of thought to the correct behaviour in this case in the context of a dive computer I designed.
The ascent profile calculated and displayed is supposed to be the one with an "acceptable chance of DCI" which, without the ceiling violation, is just the output of the ZHL decompression model I was using.
However in the case of a ceiling violation, the safest profile to display could be anything from "the violation is so trivial that it doesn't really matter", through "if you lower your GFs a little (how much?), and recalculate you'll be ok" to "given that ceiling violation, the damage is done and there's no way you're avoiding a hit so ascend directly to the surface and call for help immediately".
The problem here is that there is no relevant theory to guide us, so the computer is pretty much forced to assume the worst. So, what sense does it make to display ZHL's output since it is "strongly suspected" to be on the dangerously short side of the ascent profile with acceptable chance of DCI?
I had about the same experience quite some time ago. This was back in the day when most people did not use computers for deco diving. My buddy and I were doing a dive using written dive plans based on VPM. He had just purchased a dive shop, and Suunto had given him their new tech computer, the HelO2, to try out. He decided to take it with us to try it. He adjusted its settings to get it as close as possible to the VPM +2 settings we were using, and they really should have been pretty close to begin with.
Once we were ascending, we saw the problem that everyone experienced in those transition years of using a computer along with a written plan--which one are you really following? We followed the written plan, and the Suunto was not happy with it. It went into gauge mode during one of our deco stops, providing us no guidance. Fortunately, we were following our written plan anyway, so no harm was done, but if we had been depending on it and had not followed it because of some sort of problem in the dive, we would have been in trouble.
Kinda with you on that, that is bad. A couple I met this trip just a few days ago who were diving Nitrox 32% with air set in their computers and got locked out in the water. I tried to explain to them the illogical concept of tricking your computer as a safety pad but it went in one ear and out the other. So they just continued to dive with nothing.
GreggS
Contributor
Exactly. Even if they wanted to have that "margin of safety", why would they not surface before the computer goes into deco.? If you're trying to fool the computer, but still think you have more time for your dive, you're only fooling yourself.
And then to dive with it locked out? Yep, pretty dang stupid.
Bento.Box
Registered
I agree, but this sounds like a bug to me.
Never experienced that with my Suuntos.
The only one that went into lock mode was the Zoop. It failed to switch to dive mode when diving and after a while, it just displayed error. Battery was ok during the dive before, but later showed "low battery". Fortunately, I always dive with 2 computers and only one of them is on my MEL when buddy-diving.
How did they got locked out IN the water?
Obviously, getting the gas mix wrong is stupid and dangerous (PO2 indication and alerts will be wrong), but otherwise it shouldn't lock if followed, especially not in the water.
mrtechbench
Contributor
It is quite clear in the Suunto manuals. For example, in the D9 manual, on p78, iot says:
"The Error Mode results from omitted decompression, i.e. when you stay above the
ceiling for more than three minutes. During this three-minute period the Er warning is
shown and the audible alarm beeps. After this, the dive computer will enter a permanent
Error Mode. The instrument will continue to function normally if you descend below
the ceiling within this three-minute period.
Once in the permanent Error Mode only the ER warning is shown in the center window.
The dive computer will not show times for ascent or stops. However, all the other
displays will function as before to provide information for ascent. You should immediately
ascend to a depth of 3 to 6 m [10 to 20 ft] and remain at this depth until air
supply limitations require you to surface.
After surfacing, you should not dive for a minimum of 48 hours. During the permanent
Error Mode, the Er text will be displayed in the center window and the Planning Mode
will be disabled."
I have underlined the critical part.
This is how (from the user manual for the DX):
So, if you are slightly above the stop for more than 3 minutes, the computer locks you out DURING THE DIVE.
Regards,
- brett
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