Will a liberal computer ever go into deco before a more conservative one?

[DazedAndConfuzed]

Hi,

I have a Mares computer that uses the more conversative Wienke RGBM algorithm and a backup Aeris that uses the more liberal Modified Haldanean algorithm. In almost all the cases, I would see less NDL time on the Mares computer, but in one situation on my trip, I looked at the Aeris and saw the deco stop sign displayed (to be fair, on another dive, the Mares beeped and told me to do a deco stop too). I knew it couldn't be a fluke since only a day or two ago, my wife who uses an Aeris told me she saw this extra thick bar at the nitrogen loading graph, which never having seen that on my recently recommissioned Aeris, thought she was seeing things. On that dive, neither of my dive computers went into deco mode.

I use to dive with just one computer, but dug the old one out just to use it as backup. Plus, much of the dives we stayed deep for relatively long, where in many places, going deeper just meant seeing the same thing, only darker and bluer, this trip, one has to linger in the deep to catch the pelagics.

 

[tbone1004]

this is why we recommend that if you are using a backup computer it uses an identical algorithm to your primary or you run it in gauge mode and us it as a bottom timer.

Algorithms are funny beasts and depending on the profiles depends on how they calculate nitrogen loading. It all depends on how many tissues it is calculating and what gradient factor the algorithm is programmed for. Conservation is only relevant within the same exact algorithm and can't be compared to other algorithms regardless of how "conservative" it says it is.

Unfortunately it isn't the answer you want, but if one of them has a gauge mode and you aren't doing decompression, just carry a set of tables with you and switch one to gauge mode.

 

[stuartv]

Conservation is only relevant within the same exact algorithm and can't be compared to other algorithms regardless of how "conservative" it says it is.

Huh. Apparently, nobody told Scuba magazine that you can't compare "conservation" of the different algorithms.

SCUBALAB 2014: Dive Computer Review | Scuba Diving

dive computers: scuba gear reviews | Scuba Diving

 

[tbone1004]

Clarify, you can't compare a computer that is on "conservative" with one that is on "liberal" if they are running different algorithms, unless you go in and actually simulate dives with something like V-planner. The point of that sentence was if your computer gives you three conservation settings they don't necessarily mean the same thing across platforms. Those reviews also didn't publish the graphs of the dive profiles and the computers outputs at those times mainly because the algorithms for many are locked down and proprietary and they don't tell you what they are.



These graphs are how you compare the algorithms, and unfortunately if your computer isn't on there or one with an identical algorithm you can't plot the graph. By this chart the OC1-Z+ is more conservative at the beginning of the dive than the Galileo Luna until 60ft, then it becomes more agressive from 60 ft until the end of the dive. This is why without having the actual algorithm and plotting theoretical dive profiles, or having computers running identical dives and marking their NDL's throughout the dive profile, you can't directly compare what is said to be "conservative" vs is what isn't.

ediving.us ? View topic - Fine Tuning a Decompression Algorithm

good article there. Conservative means different things, it can mean less bottom time, it can mean same bottom time longer time to surface, can be a more linear graph of nitrogen intake or it could be very nonlinear etc, it's generally nonlinear and because the algorithms are different and most of the time with recreational computers you don't always have the actual algorithm to put into something like Vplanner, you can't always predict what it is going to do. Even if the area under the curve is the same, a more conservative computer can give you longer NDL's at 50ft, but shorter NDl's at 80ft, but it is still considered more conservative than one that gives you slightly less or equal time at 50ft, but more ndl deeper.

 

[DazedAndConfuzed]

this is why we recommend that if you are using a backup computer it uses an identical algorithm to your primary or you run it in gauge mode and us it as a bottom timer.

Algorithms are funny beasts and depending on the profiles depends on how they calculate nitrogen loading. It all depends on how many tissues it is calculating and what gradient factor the algorithm is programmed for. Conservation is only relevant within the same exact algorithm and can't be compared to other algorithms regardless of how "conservative" it says it is.

Unfortunately it isn't the answer you want, but if one of them has a gauge mode and you aren't doing decompression, just carry a set of tables with you and switch one to gauge mode.

I dont want to use the Mares in Gauge mode since it is AI. The Aeris seem to have gauge mode only if I come back to the surface with a violation, or as I found out on a dive, I descended without waking it up and it was only showing the depth. Pressing a button to wake it up made it freak out. The Aeries in on the wrist, is more convenient, but want to be able to see more than just the depth. Most likely, I would just ignore its NDL time, and if it does tell me to do a deco stop, take it as an extra precaution (although on the Aeris, the deco stop goes away if I ascend to shallower depth and continue diving, while on the Mares, it is mandatory, even if it is a 10ft stop and my dive does not end for another 30 minutes).

 

[tbone1004]

sounds like the Mares has to go to gauge mode. Even with it being AI, that has essentially nothing to do with your tissue loading, so it should still read out your tank pressure, depth, and dive time, just doesn't turn on the decompression calculations and give you NDL's. Not familiar with the computer, but I imagine it would also still give you your ETA at the surface based on your air consumption and dive profile.

 

[DazedAndConfuzed]

Clarify, you can't compare a computer that is on "conservative" with one that is on "liberal" if they are running different algorithms, unless you go in and actually simulate dives with something like V-planner. The point of that sentence was if your computer gives you three conservation settings they don't necessarily mean the same thing across platforms. Those reviews also didn't publish the graphs of the dive profiles and the computers outputs at those times mainly because the algorithms for many are locked down and proprietary and they don't tell you what they are.

View attachment 194880

These graphs are how you compare the algorithms, and unfortunately if your computer isn't on there or one with an identical algorithm you can't plot the graph. By this chart the OC1-Z+ is more conservative at the beginning of the dive than the Galileo Luna until 60ft, then it becomes more agressive from 60 ft until the end of the dive. This is why without having the actual algorithm and plotting theoretical dive profiles, or having computers running identical dives and marking their NDL's throughout the dive profile, you can't directly compare what is said to be "conservative" vs is what isn't.

ediving.us ? View topic - Fine Tuning a Decompression Algorithm

good article there. Conservative means different things, it can mean less bottom time, it can mean same bottom time longer time to surface, can be a more linear graph of nitrogen intake or it could be very nonlinear etc, it's generally nonlinear and because the algorithms are different and most of the time with recreational computers you don't always have the actual algorithm to put into something like Vplanner, you can't always predict what it is going to do. Even if the area under the curve is the same, a more conservative computer can give you longer NDL's at 50ft, but shorter NDl's at 80ft, but it is still considered more conservative than one that gives you slightly less or equal time at 50ft, but more ndl deeper.

The Mares Puck Air and Oceanic OC1 (which along with the Aeris, both uses the liberal Pelagic DSAT algorithm) are at the extreme ends of each other, which even in their simulation, never even got close to each other. So I don't know under what situation this the much more 'liberal' computer went into deco earlier than the much more 'conservative' one.

sounds like the Mares has to go to gauge mode. Even with it being AI, that has essentially nothing to do with your tissue loading, so it should still read out your tank pressure, depth, and dive time, just doesn't turn on the decompression calculations and give you NDL's. Not familiar with the computer, but I imagine it would also still give you your ETA at the surface based on your air consumption and dive profile.

Don't think I will be doing that. The Aeris was my computer that I handed down to my wife, when I got the next Aeris, which I gave to her again when I got the Mares. Instead of it sitting around, I thought I could use it to replace my bottom timer that disappeared from my luggage after it was inspected by TSA. The Aeris computer is old and missing some features, which is the reason I replaced it many years ago.

 

[stuartv]

Clarify, you can't compare a computer that is on "conservative" with one that is on "liberal"

The OP didn't ask about having a computer "on conservative". He just asked about a liberal computer going into deco before a more conservative computer.

 

[victorzamora]

One thing to mention is that one computer can be more liberal on a square profile, and penalize you hard (and unpredictably) for yo-yo or sawtooth profiles or short SIs. Even if ScubaLabs DID produce those pretty charts, it doesn't mean that's the case for all types of diving. The only way around it would be to put your "main" computer in "ultra conservative" mode to verify that you won't go into deco on your backup OR to be running identical algorithms. Otherwise, you need a bottom timer and some tables (or dive planner on your primary).

One more thing to mention: The most dangerous aspect of, and my biggest problem with, AI computers is that they tend to induce complacency. So, if you're trying to keep your AI computer connected just so you can have the "Air Time Remaining" or whatever they call it, be aware that that could get you killed. It's FAR too liberal for any real world scenarios as it doesn't even try to compute air-sharing or panic into its calculations.

PS- Mares is one of the companies that uses the goofy, proprietary, unpredictable algorithms that randomly punishes you for stuff you can't foresee.

 

[RonR]

Hi,

I have a Mares computer that uses the more conversative Wienke RGBM algorithm and a backup Aeris that uses the more liberal Modified Haldanean algorithm. <snip>

RGBM itself is not inherently conservative or liberal, it&#8217;s a framework that provides handles with which individual manufacturers can build in greater or lesser levels of conservatism. Because Suunto tends to be very conservative, many think RGBM is- but that is just Suunto's implementation, others are not the same.


You don&#8217;t mention anything much about the prior dive history or the profiles involved. Some computers may be more conservative when dealing with repetitive or multi-day profiles, deeper than previous dives, and so forth. They might be more liberal in single dive NDL's. Simplistic comparisons based on single dive profiles, or even just a few, don&#8217;t really capture the potential for variation. It's a lot more complex- what if a computer puts you into deco slightly earlier, but then gives a shorter time to surface than another computer? Which is more conservative?


To copy my standard response on the subject:
Conservatism in dive computers is hard to nail down, but differences between computers tend to seem more extreme in shallower, longer dives, because we treat deco/ no deco as a binary function when in reality is is a gradually increasing slope- very gradually increasing at shallow depths. So on shallower dives even a slight divergence in the algorithm conservatism can translate into many minutes more or less of no-deco time. The same computers might show much less difference- in minutes of no-deco time- at deeper depths. That probably accounts for some of the subjective differences in experience of how conservative a particular computer is.

Computers that show only a minute or two difference on a deep dive might diverge by many minutes on a shallow one. What you don't see is that one is "almost" in deco, and the other is "barely" in deco. They may not be, in mathematical terms, very far apart at all, but because they treat deco/ no-deco and a binary switch, one seems much more conservative. If it were displayed in analog terms, as say a % of risk, they might not seem very different.

A lot of divers see no-stop limits as falling off a cliff. But it's a lot more like hikers climbing a very gradually increasing slope, and deciding at what % grade to turn back. If one person decides to turn back at 30% and another at 32% grade, and they both head straight uphill, they will turn around at almost the same time. If they traverse the slope at a very shallow angle, the 30% hiker may turn around a long time before the 32% hiker. His turnaround point is no more conservative than it was going straight uphill, his risk no greater, but the difference in minutes between the two is greater because of the angle at which they approached the hill.

Ron