Why are my Vytec and Cobra so different?
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The issue isn't 107' for 18 or 20 minutes Karl... as you said.. its only 15 minutes. Its the first post in your first thread on this subject. No doubt the suunto is more conservative over 1.4 po2 as well it should be I believe. Safety and squemish aren't the same thing Karl. I don't see you doing that dive... you act like its so hard for you to find 107' of water, but you just did a dive much deeper than that. If you wanted to prove your point you would have taken the vyper down with you and provide the evidence. I will be glad to do the dive that was in the original post. Since Ari is neutral, let him set the stage for the dive/dives.
The faster rate, as anyone with a suunto can easily see for themselves, experiences no acceleration. The rate at which the OLF bar graph grows remains the same given the same depth. 15 minutes at 107 or 18 minutes at 110, no matter how you look at it, the rate remains constant throughout each dive. Sitting at 107', it never suddenly starts racing ahead. You have plenty of time to see that the your OLF graph is filling up. If you pay any attention to your cobra or vyper during the dive, you can tell at what rate the graph is filling up. You have 10 segments... surely you can pick up on it sometime during the 15 or 20 minutes you're sitting at depth.
The faster rate, as anyone with a suunto can easily see for themselves, experiences no acceleration. The rate at which the OLF bar graph grows remains the same given the same depth. 15 minutes at 107 or 18 minutes at 110, no matter how you look at it, the rate remains constant throughout each dive. Sitting at 107', it never suddenly starts racing ahead. You have plenty of time to see that the your OLF graph is filling up. If you pay any attention to your cobra or vyper during the dive, you can tell at what rate the graph is filling up. You have 10 segments... surely you can pick up on it sometime during the 15 or 20 minutes you're sitting at depth.
Give the vytec thing a break Karl. We all know that the vytec is built to be more liberal than any other suunto model, not just the cobra or vyper. So there's no real point in continually saying the cobra and vyper should be as liberal as the vytec. That is really all that you're saying. You expect the cobra and vyper to be as liberal as the vytec and its simply not at all. There's no news there ace. Suunto never claimed they were. The did state that these models are much more conservative when you reach a po2 of over 1.4 (107' is technically over 1.4 since we know they round up). 106', now thats less than 1.4 so its rounded up to 1.4, but not over. Right guys? Thats whats already been stated over and over again. Thats no bug... its how it was designed... to be conservative... you can't argue that.
truly don't understand.
Let me try to explain it one more time.
The Suunto Cobra and Vyper have two issues:
1. They have a rounding error where they believe you have reached a 1.4 PO2 before you actually have; that is, the part that computes CNS loading disagrees on the PO2 with the part that alarms when you exceed a 1.4 setpoint. This results in the "acceleration with no alarm" at 107'.
2. They accelerate the CNS clock radically any time you exceed a 1.4 PO2 setpoint, whether you do so intentionally (e.g. you've selected a 1.5 or 1.6 setpoint for the dive) or not.
This makes a mockery of the ability to set a PO2 setpoint over 1.4, in that the computer will instruct you to turn a dive on CNS loading in about EIGHT minutes (the point where you have reached the halfway point) on CNS load when you exceed or closely approach a 1.4 PO2 setpoint.
This is grossly inappropriate behavior for the computer to display.
The Vytec DOES NOT do this. In fact, the Vytec remains "sane" about the CNS loading up to a 1.6 PO2. It does indeed load more quickly at PO2s beyond 1.4, but the acceleration is "sane" and in accordance with commonly-accepted exposure limits for that PO2. Beyond that IT does the "gross acceleration thing", but that's quite justified - 1.6 is a PO2 beyond which you simply should not go.
But to impose the 1.4 PO2 limit even when you have told the computer you prefer a higher setpoint is inappropriate.
As for me doing a 107' sand dive just for grins and giggles, I don't believe it is necessary to prove the point; the acceleration has already been proven; that the profile I posted is not "clean" in that there is an excursion below the MOD subsequent to the point on the profile where the acceleration is already evident does not impugn the data to that point, which shows PRECISELY the behavior that the simulator predicts.
Let me try to explain it one more time.
The Suunto Cobra and Vyper have two issues:
1. They have a rounding error where they believe you have reached a 1.4 PO2 before you actually have; that is, the part that computes CNS loading disagrees on the PO2 with the part that alarms when you exceed a 1.4 setpoint. This results in the "acceleration with no alarm" at 107'.
2. They accelerate the CNS clock radically any time you exceed a 1.4 PO2 setpoint, whether you do so intentionally (e.g. you've selected a 1.5 or 1.6 setpoint for the dive) or not.
This makes a mockery of the ability to set a PO2 setpoint over 1.4, in that the computer will instruct you to turn a dive on CNS loading in about EIGHT minutes (the point where you have reached the halfway point) on CNS load when you exceed or closely approach a 1.4 PO2 setpoint.
This is grossly inappropriate behavior for the computer to display.
The Vytec DOES NOT do this. In fact, the Vytec remains "sane" about the CNS loading up to a 1.6 PO2. It does indeed load more quickly at PO2s beyond 1.4, but the acceleration is "sane" and in accordance with commonly-accepted exposure limits for that PO2. Beyond that IT does the "gross acceleration thing", but that's quite justified - 1.6 is a PO2 beyond which you simply should not go.
But to impose the 1.4 PO2 limit even when you have told the computer you prefer a higher setpoint is inappropriate.
As for me doing a 107' sand dive just for grins and giggles, I don't believe it is necessary to prove the point; the acceleration has already been proven; that the profile I posted is not "clean" in that there is an excursion below the MOD subsequent to the point on the profile where the acceleration is already evident does not impugn the data to that point, which shows PRECISELY the behavior that the simulator predicts.
Charlie99
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What you are saying above should be no surprise. The VyTEC manual says it follows NOAA 1991 limits up to 1.6 bar. The Cobra and VyPER manual say it follows NOAA 1991 limits up to 1.4 bar and that "the limits above 1.4 bar are significantly shortened". They don't say what "what significantly shortened " is. You say it about about 1/10 of NOAA limit.
While you don't like what it is doing, it looks to me like the VyPER and Cobra are doing what the manual says they do. I wouldn't use them, since I also am willing to exceed 1.4 ata ppO2 for short periods, but it's not a bug when it just doing what it says it does. It does indeed "make a mockery" of being able to set the alarm at 1.6 bar ppO2, but that's the design.
Note that the manual also refers to BAR,which is 1.3% less than one atmosphere (1013.25 = 1ata). That might be why it is going to "significantly reduced limits" a foot or so before you expect it. Karl: if this discrepancy disappears when running in the metric mode,then the problem might be that they used the classic MOD = 4620/EAN-33 formula to get the MOD alarm setting in ata, but use bar in the actual CNS clock calculations.
Extraneous note: the Vyper says that it decays the CNS O2 loading with a 75 minute halftime, not the 60 minutes I stated in an earlier post. I thought I saw 60 minutes in some Suunto manual, but it's not the Vyper.
I understand all of that, but the definition of "significantly shortened" does not give someone an expectation of 1/10th of the original time!
The CNS O2 single-exposure limit at 1.6 PO2 is "significantly shortened" (90 minutes .vs. 150) over that at 1.4.
To go even a bit further in the quest for conservatism seems reasonable. To shorten it to 1/10th of the original time, and to do it all at once as if a switch was thrown, is not!
The problem here is not necessarily that it might provoke a rapid ascent if you got "surprised" by this (although it might!) The bigger issue is that this misfeature makes O2 load tracking close to useless on these computers.
It is virtually impossible to run out of O2 clock time (either CNS or pulmonary) diving at a PO2 under 1.4. However, it is not at all impossible to do so diving at a PO2 exceeding 1.4; in fact, it is a very real consideration if you are heavily diving Nitrox (say, on a liveaboard) and using the "NDL expansion" that Nitrox provides somewhat aggressively.
It is precisely in those circumstances that you need the computer to display accurate information, and it is precisely under those circumstances that you cannot count on it to do so.
The CNS O2 single-exposure limit at 1.6 PO2 is "significantly shortened" (90 minutes .vs. 150) over that at 1.4.
To go even a bit further in the quest for conservatism seems reasonable. To shorten it to 1/10th of the original time, and to do it all at once as if a switch was thrown, is not!
The problem here is not necessarily that it might provoke a rapid ascent if you got "surprised" by this (although it might!) The bigger issue is that this misfeature makes O2 load tracking close to useless on these computers.
It is virtually impossible to run out of O2 clock time (either CNS or pulmonary) diving at a PO2 under 1.4. However, it is not at all impossible to do so diving at a PO2 exceeding 1.4; in fact, it is a very real consideration if you are heavily diving Nitrox (say, on a liveaboard) and using the "NDL expansion" that Nitrox provides somewhat aggressively.
It is precisely in those circumstances that you need the computer to display accurate information, and it is precisely under those circumstances that you cannot count on it to do so.
Suunto needs to do something about this disparity. They must realize that a fair number of people will use the Vytec and Cobra together, simply because they are identical in function but for the fact that the Vytec is hoseless, and it allows you to input three different mixes and switch during the dive. Showing 80% 02 exposure on one model and 20% on another after identical profiles is not kosher, IMO.
Is there a reason that neither Jamie nor Karl has uploaded a Suunto Dive Manager file that shows the profile they used? It seems it would be a trivial matter and would likely help reduce the head bashing that has gone on here... you would both be able to see exactly what dive profile was followed by the other in testing...
You wouldn't have to. Save your log as another filename then delete all but the dives in question. Didn't know that this was such a crazy idea...
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