Conservative settings on Mares computers

[dmaziuk]

VPM is available, though I haven't spent enough time looking at it to try and understand any of it. I think it's moot, though, because the statement was "I understand the risk factors". I read it on the Internet that Shearwaters in "tec" mode will follow the model to the letter and ignore missed stops and ascent rate violations etc. IMO that's the only case where you understand what the computer is doing -- which is not quite the same as risk factors of using that particular computer.

If you're talking Mares RGBM, you probably mean recreational computers that don't need to match a detailed dive plan because we don't plan rec dives that way. Compare it to other recreational computers: DSAT or "Buhlmann" PZ+. Do you have any idea what PZ+ is doing?

 

[Dennis Guichard]

I have the Giotto. The VBM at 5 is the closest match to the Giotto with no conservative settings. And yes, the Cressi and Mares are both considered very conservative after the first dive of the day.

There's some dive profiles you can download from Scuba-Lab in the USA where they tested a range of computers in a chamber side by side to have a look at what sort of liberal or conservative settings they might each be programmed to - the Cressi computer they tested (the Goa) has a 9-tissue 'modified' RGBM algorithm in it (which may be similar or wildly different to your Giotto), and it's just interesting to see how conservative it seems to be on single and repetitive recreational dives!? The dived all the computers next to two Shearwater computers, the one with GF set at 45/85 and the other one at its 'least conservative setting' (which I assume is somewhere near 95/95)... on the 4th dive when the Perdix 45/85 was permitting 34 minutes bottom time at 18m the Cressi was only allowing 25 minutes.

All the computers naturally 'dived' the same multi level chamber profile with the same ascent rates and stops - no one of course know which algorithm is 'right or wrong' of course as yes they are all largely hypothetical models, but it's just valuable and interesting to see where any computer you're using might sit on that line from liberal to conservative...?

All the computers using the 16-tissue RGBM or Buhlmann algorithms ran about the same as one another, after/during the four dives, but all well within the allowable 45/85 Perdix limits. The Cressi using a 9-tissue modified RGBM algorithm was extremely conservative, whilst the computers running DSAT algorithms were very liberal on par with the Perdix.

I just think that if you understand your computer, whichever model you're using, then you're better informed when it comes to pushing it to its limits of allowable bottom time or whether (personal factors considered i.e. age, overweight, unfit, fatigued, etc) it is better to dive it more conservatively by choice?

(11 New Dive Computers Tested By ScubaLab In 2017) - look for the downloadable chamber data link...

 

[Dennis Guichard]

What I suspect happens is that ALL the sports diving recreational dive computers are purposely set to be on the conservative side to keep sports divers safer? Whereas I understand the 'more advanced' Perdix computers might run a pure Buhlmann algorithm that the user then freely sets according to their own personal level of conservatism/risk? I understand the RGBM computers typically also become 'more conservative' with repetitive multi-day dives because they're calculating for free phase asymptomatic micro bubbles so that's something I found interesting with this test how the Buhlmann and RGBM computers actually ran pretty much to the same bottom times.

If I was diving a Mares Quad I'd feel comfortable personally to dive it to its limits of allowable bottom time but I wouldn't do that with a Sherwood or Cressi to the same degree knowing the above? The Cressi Goa seriously penalises divers on allowable bottom times so it wouldn't be ideal for a week in the Red Sea?

I believe that sports divers typically just buy whatever computer is on 'special' in the dive shop and dive that to whatever it's allowable limit is, trusting it emphatically, but not ever really understanding much around the risks they might be playing with it?

 

[dmaziuk]

There's a very simple rule in signal processing: if you want to adequately recreate a signal, you need to sample it at twice its frequency, or better. With the fastest compartment having half-time of 4 minutes, the comparisons would've been half-meaningful comparison if they recorded NDLs every 110 seconds throughout all dives. Otherwise all their numbers are good for is pulling wool over the eyes of naive readers. There is a name for it: spotlight fallacy.

I believe that sports divers typically just buy whatever computer is on 'special' in the dive shop and dive that to whatever it's allowable limit is, trusting it emphatically, but not ever really understanding much around the risks they might be playing with it?

I'm not sure I follow the logic of this since to me "more conservative" in this context means "less risky" and so I'd be more worried buying a ZHL or DSAT computer than the Mares.

 

[rongoodman]

VPM is available, though I haven't spent enough time looking at it to try and understand any of it. I think it's moot, though, because the statement was "I understand the risk factors". I read it on the Internet that Shearwaters in "tec" mode will follow the model to the letter and ignore missed stops and ascent rate violations etc. IMO that's the only case where you understand what the computer is doing -- which is not quite the same as risk factors of using that particular computer.

The Shearwaters most certainly don't "ignore" missed stops, but they will not lock you out because of them. They will present warnings which require your acknowledgement and make adjustments as best they can.

 

[Neilwood]

What I suspect happens is that ALL the sports diving recreational dive computers are purposely set to be on the conservative side to keep sports divers safer? Whereas I understand the 'more advanced' Perdix computers might run a pure Buhlmann algorithm that the user then freely sets according to their own personal level of conservatism/risk? I understand the RGBM computers typically also become 'more conservative' with repetitive multi-day dives because they're calculating for free phase asymptomatic micro bubbles so that's something I found interesting with this test how the Buhlmann and RGBM computers actually ran pretty much to the same bottom times.

If I was diving a Mares Quad I'd feel comfortable personally to dive it to its limits of allowable bottom time but I wouldn't do that with a Sherwood or Cressi to the same degree knowing the above? The Cressi Goa seriously penalises divers on allowable bottom times so it wouldn't be ideal for a week in the Red Sea?

I believe that sports divers typically just buy whatever computer is on 'special' in the dive shop and dive that to whatever it's allowable limit is, trusting it emphatically, but not ever really understanding much around the risks they might be playing with it?

Having dived with a Giotto in the Red Sea in 2016, I can say that I did not find it limiting dive times. I suspect this is down to dive times of less than 1Hr and no deeper than 25-30m along with fairly long surface intervals (2-3hrs in general). Had the SI been shorter I suspect it might have limited things a lot more.

 

[npole]

My buddy own a Giotto, and 1/3 of times, she fells into deco when my Perdix AI has like 30 minutes of NDL at the same deep, when we do multiple dives with minimum surface interval (60 minutes).
In many occasions she's forced to dive a couple of meters above me to not being forced to do a deco stop (or being locked out by the Giotto).
The computer is set on the most permissive setting... but I think it's a way too conservative (or my Shearwater is too permissive, despite the different algo..).

 

[dmaziuk]

The Shearwaters most certainly don't "ignore" missed stops, but they will not lock you out because of them. They will present warnings which require your acknowledgement and make adjustments as best they can.

When I say "ignore" I mean just recalculate your gas loading based on your new depth and time. There is nothing else in Shreiner's equation. Bubble model may decide that your bubbles have grown too big to off-gas effectively and you now need to pad you SI to let them get re-absorbed first. Then you off-gas at the Shreiner-prescribed rate. Blow the ascent rate and SI for a couple of dives in a row and your bubble-model computer is suddenly "way too conservative".

Of course that's just a hypothesis off the top of my head, I've really no idea what I'm talking about.

 

[Michael Krabbe Borregaard]

Sorry for bumping the old thread, but I couldn't help noticing that the original question was never answered, which isn't so useful for people coming across this thread later. Do any of the clearly very knowledgeable people here know what difference the P1 and P2 conservative settings on the Mares computers actually make?

 

[KenGordon]

Sorry for bumping the old thread, but I couldn't help noticing that the original question was never answered, which isn't so useful for people coming across this thread later. Do any of the clearly very knowledgeable people here know what difference the P1 and P2 conservative settings on the Mares computers actually make?

It is probably like table 6.1 here

https://ns.suunto.com/Manuals/Zoop/Userguides/Suunto_Zoop_UserGuide_EN.pdf

For example NDL at 30m is 18 minutes in P0, 14 for P1 and 12 for P2

Note that there is a lot of rubbish in this thread, and generally on SB, comparing GF with RGBM etc. You really cannot. For example on Saturday I did a simple 20m dive with a Zoop on P0 and Perdix on medium. For most of the dive the Zoop was showing a longer NDL than the Perdix, but at the end when much shallower the Perdix was showing more than the Zoop. This will be because a different compartment was now limiting. That demonstrates that the profile is important and it is not as simple as made out. There really is no GF setting which is equivalent to any given RGBM setting, DSAT, PADI table, BSAC table or anything with different compartments.