Conservative settings on Mares computers

[Dennis Guichard]

Does anyone happen to know what the P0 (standard setting / least conservative), P1 & P2 (most conservative) settings actually influence or refer to in the range of Mares dive computers?

It would be helpful to understand if anyone can relate that to comparative gradient factors - I KNOW the Mares use RGBM algorithms and GF's relate to Bulhmann ones but I saw a conversation on another thread about a Suunto Vyper that was dived alongside a Shearwater one and the guy had to set a high GF of 95% to match the Vyper no-stop dive times.

Mares don't seem to give ANY indication anywhere that I can source that actually divulges anything around what those settings relate to, which in not very helpful...?

Thanks in advance, kindest regards, Dennis

 

[uncfnp]

I doubt you will get too much useful info here since the RGBM and Bulhmann algorithms are so very different. I find it very odd that a diver had to set the Shearwater to High to match the conservative setting on any computer running RGBM but I am not familiar with the vyper. I do dive a Cressi (RGBM) and a Shearwater but use the VPM algorithm on the Shearwater. I am able to get a close match with the Cressi set to most liberal and the Shearwater VPM to most conservative.

 

[Dennis Guichard]

shitballs... you know when you saw an interesting comment somewhere and then hours later you try and remember where it was you saw it... and of course you can never find it or remember... well I've just spent probably two hours going through my Internet history to find this blooming message again... :-D (that's old age for you!?)

One problem is that many 'recreational' models change parameters over repetitive dives. RGBM is a good example of that.

I did some dives with my Shearwater and Suunto Vyper on the same arm. I could change the Shearwater GFhi in-water, so I used that ability to match the RGBM bottom times over several deepish rec dives.

On the first dive, it took GF95 to match the bottom time given by RGBM. On the second dive, I had to drop to GF65 to get a matching bottom time.

Setting a high GFhi for recreational dives makes sense for solitary dives, but do consider dialing it down somewhat for repetitive dives.

For recreational dives, the GFlo should be set very high. If you don't go into deco, then GFlo has no impact. However, if you accidentally go into deco... then you'd want a simplistic ascent and shallow stops. Keep it simple and do 'emergency' deco where your gas will last longest.

 

[Dennis Guichard]

GFhi95 equivalent is quite 'high risk' I think for a consumer recreation computer if that's the comparison against a Buhlmann gradient factor? I find it easy to understand risk factors around GF's but with the typical P0, P1 & P2 'conservative settings' on RGBM computers (like the Mares or others) it's very difficult to understand where they sit on any risk scale because there's very little information seemingly in what those relate to and/or how conservative/liberal any recreational computer is anyway? I'm guessing that with Bulhmann + GF's you get a consistent 'level of self-set risk' across multi-day diving whereas with recreational RGBM type computers they are varying the risk of their own accord based on their free phase theories of bubble formation and sizes? (Q. isn't that a lot of what VPM measures and what their algorithms are based on?)

 

[Dennis Guichard]

I doubt you will get too much useful info here since the RGBM and Bulhmann algorithms are so very different. I find it very odd that a diver had to set the Shearwater to High to match the conservative setting on any computer running RGBM but I am not familiar with the vyper. I do dive a Cressi (RGBM) and a Shearwater but use the VPM algorithm on the Shearwater. I am able to get a close match with the Cressi set to most liberal and the Shearwater VPM to most conservative.

Thanks for your feedback which I appreciate, which Cressi do you have? It seems then that the Cressi in its default setting is VERY conservative compared to your Shearwater in it's default VPM setting? The VPM and RGBM algorithms are both dual phase so you'd think they would both give similar outputs?

 

[uncfnp]

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.

Devon’s observations show why trying to match RGBM to Bulhmann just doesn’t work. The are too many variables to the RGBM that do not apply to Bulhmann.

 

[rongoodman]

The problem with this discussion is that there is no way of knowing what "RGBM" actually means, since it's just a proprietary label licensed by the companies. It probably isn't an actual full implementation of the RGBM model. It's unlikely that a recreational computer would have the power to do so.

 

[uncfnp]

The problem with this discussion is that there is no way of knowing what "RGBM" actually means, since it's just a proprietary label licensed by the companies. It probably isn't an actual full implementation of the RGBM model. It's unlikely that a recreational computer would have the power to do so.

But that is not unique to RGBM. My understanding is that many recreational dive computer manufacturers use adapted versions of the algorithms, be it RGBM or Bulhmann.

 

[dmaziuk]

GFhi95 equivalent is quite 'high risk' I think for a consumer recreation computer if that's the comparison against a Buhlmann gradient factor? I find it easy to understand risk factors around GF's

You do? I have e.g. not seen anytning about ascent rate in either Buhlmann's+GF or Shreiner's equations, yet from my experience with carbonated beverages I'm pretty certain the rate of depressurization is very much a risk factor. So with Buhlmann+GF any risk related to rapid ascents is either not factored in, or programmed as some unknown add-on on the side by the manufacturer. At least bubble models are supposed to have bubble formation designed in from the start...

 

[Neilwood]

You do? I have e.g. not seen anytning about ascent rate in either Buhlmann's+GF or Shreiner's equations, yet from my experience with carbonated beverages I'm pretty certain the rate of depressurization is very much a risk factor. So with Buhlmann+GF any risk related to rapid ascents is either not factored in, or programmed as some unknown add-on on the side by the manufacturer. At least bubble models are supposed to have bubble formation designed in from the start...

That is the problem though - bubble models are supposed to factor those things in but no one apart from the manufacturer actually knows because the algorithms are not in the public domain. It is very hard apart from using the manufacturers desktop dive planning software (if available) to see what effects actions might have. During a dive I have no idea what penalties it might add to my dive or subsequent dives because I don't know how it is written.

Buhlman+GF is however in the public domain and there are a number of packages where it is possible to accurately match dive plans between the dive computer and the desktop version.

Of course with any algorithm, the obvious needs stated - all they can give you is a theoretical prediction that shouldn't bend you. Measure with a micrometer, mark with chalk and cut with an axe. The computer gives a line in the sand based on any number of variables but how accurate that is to the individual on any given day is guesswork.

@Dennis Guichard the only people who know how Mares implemented RGBM are Mares.