So, who is going to market an inexpensive rec computer running Buhlmann with GF?

[RonR]

....
Why does the Cobalt phase in the full RGBM algorithm with depth, rather than just run it all the time?

Full RGBM is very computationally intensive. It doesn't provide things that recreational divers want- it doesn't give you no-stop times, for instance, so you are back to using M-values to provide the information most recreational divers are most interested in. It really only comes into play for calculating deco schedules.

-Ron

 

[RonR]

I'm curious how much of the popularity of RGBM is based on, "well we paid for it, we might as well use it." I can't imagine licensing it from Bruce Wienke was cheap.

Until there's a financial reason to divest themselves from RGBM, they might as well keep using it. I don't think recreational divers are any more prone to getting bent by using it, so it's not like there's a safety-driven reason to dump it (or really any other modern algorithm). I don't know any technical divers that are doing serious dives with RGBM anymore. Light deco, sure, but 6 hours in a cave or 120m on the Britannic, I don't think it's much of a contender at all. Not to say it's not used, just that it's probably nowhere near as prolific in the technical diving world as it was 10 years ago or so.

Sure, an old-style Zoop (that novo stuff can go kick rocks) running Buhlmann-GF would be fantastic, but I don't see a reason why Suunto would ever go that direction. There's just no need. Same same for other manufacturers using whatever algorithm they've chosen.

Something important to remember is that the primary drivers of Buhlmann-GF are technical divers. They are the ones that tend to tweak stuff to suit their style. Most recreational divers probably don't even adjust the conservatism settings on their computers, let alone get into the nuts and bolts of decompression models, at least enough to understand what custom GF setting they'd like to use. And the Scubaboard audience is comparatively small, so while there may be a more knowledgable user base who would desire something like this, it's probably nowhere near large enough to get a major manufacturer to throw down a new manufacturing line.

Of course this is all just rampant speculation. @RonR would be a much better source for sure, and barring any trade secrets, I'd be interested in his insight into the continuing choice of algorithm by different manufacturers.

Also, to be clear, I think an old-style Zoop with custom GF's would make an awesome dive computer. I'd buy one for rec dives and use that instead of my Predator.

I think your post is right on. If you go back some years, there were significant differences in algorithms, and some were changed quite a lot- sometimes while attempting to cover up the fact that they had changed. But that’s all ancient history now. While diving will always have a level of risk, dive computer algorithms as currently implemented- all of them- have very good records and have worked well for many millions of dives. Once you have invested the effort to implement a particular algorithm there is little motivation to change.

The Tech community understandably is more positively disposed to an algorithm that is open and adjustable, and there are some indications that models like Buhlmann could provide better results at the fringes. But for the vast majority of divers these concerns are of little consequence. They may be helped by adding conservatism based on things like multi-day diving or multiple dives in a day. Straight Buhlmann with custom GF’s is for those who want to make their own choices.

While algorithms get a lot of attention, far more important for most divers would be aspects of the computer that are not algorithm dependent. Will it lock me out? How are things like GTR calculated? How are events like start of a dive, stop departure, safety stops, and time away from a stop handled? How are really erratic profiles handled? There are literally 100’s of questions that are not addressed by any algorithm (and don’t show up in most tests and reviews) that every dive computer designer needs to answer. The most diver friendly way to handle these situations is often very complex to program into firmware. And as a designer if you do the job well the goal is to not be noticed- except that you made something easy to use.

That said, I think a simple puck with custom GF's would be pretty cool. But it probably wouldn't increase sales for the manufacturer noticeably.

-Ron

 

[atdotde]

To be honest, it does not make much sense to give the user a lot of customisation options with regard to deco as partially everybody (including tec divers with thousands of dives) cannot make an informed decision on these things. Given that one typically aims for safety levels of roughly one accident per 10000 dives, hardly any diver has collected enough data (several times that number of dives dived at the limit of the algorithm!) to estimate the safety of their settings. In most cases it boils down to "I feel strong, so I can dive more aggressive settings than all the wimps out there". Or on the other extreme, observing that any altitude or conservatism settings on my Vyper does not get me out of the water before dinner so I don't use them.

So here is the challenge: Based on what information do you choose things like gradient factors? Did your lucky tooth tell you?

 

[rongoodman]

Full RGBM is very computationally intensive. It doesn't provide things that recreational divers want- it doesn't give you no-stop times, for instance, so you are back to using M-values to provide the information most recreational divers are most interested in. It really only comes into play for calculating deco schedules.

-Ron

Thanks for taking the time to provide this information.

 

[scubadada]

...The result is that computers that implement Buhlmann at present tend to be more full featured and technically oriented, and the higher volume / lower cost producers are still invested in the solutions they came up with in the past. There is certainly no technical reason Buhlmann with preset GF’s (I only say preset to avoid interface complications) could not be used on the most inexpensive dive computers...

Both Shearwater and Garmin offer preset GFs of 35/75, 40/85, and 45/95 in their rec modes. It was interesting to see full page ads in the August issue of Scuba Diving Magazine for both the Teric and the Descent MK1. It is pretty clear who the intended audience is, it's certainly not the technical divers on SB.

 

[dmaziuk]

I’m curious what people would think about a computer with both fully iterative RGBM and Buhlmann with GF, that had the ability to switch between and compare algorithms?

One of the OSTCs (4?) can run ZHL and VPM side-by-side, you don't even need to switch anymore. I think it's a dual-core ARM processor, I expect a quad-core should be plenty for full RGBM and ZHL in parallel. Battery life might suck though...

 

[dmaziuk]

So here is the challenge: Based on what information do you choose things like gradient factors? Did your lucky tooth tell you?

We choose one of 3 fixed presets given to us by the manufacturer. Because they, like Mom and Pop, Know Better(tm).

Seriously, I don't see how it's any different from choosing "SF" 0, 1, or 2 on my current DC. I may think I know how "GF" works, as opposed to "SF", but AFAIMC it's pretty much six of one vs. half a dozen of the other.

 

[ericBSoCal]

Speaking of presets -
I've got a Seac Guru I bought on ebay. I haven't used it yet. The GF presets are:

93/93
90/90
80/80
75/75
30/90
20/89

Depending on whether you read the ratio or the seac manual, either 93/93 or 90/90 is the default. I'm coming from a Cressi Leonardo on default settings. I'm a pretty new diver (38 dives), and mostly shore dive to 40 or 50 feet max, and haven't hit NDLs yet. I will be doing AOW within a year or so. So to atdotde's point - what information do I use to pick a GF? It sounds like the ratio/seac GFs are pretty far off OC Rec Shearwater/Garmin presets, except the last two non-linear ones, and I can use apps like MultiDeco to give me a rough idea of the difference in NDL time, but that doesn't tell me whether I'm making good choices.

 

[dmaziuk]

GF Low should not make any difference whatsoever on non-stop dives. So until you go tech. you're looking only at 75, 80, 89, 90, and 93. 93 should be close to DSAT and then you'll essentially have "SF1" @90 and "SF2" @80, and "SF3" @75. Just like your Leonardo, less "conservative". At least on "SF0".

 

[ericBSoCal]

Thanks, good to know.

Is there any app/site/article that would let me see the m-value curve as affected by gradient factors? Seeing the results of gradient factors in a deco schedule only really gives me a rough idea of the intersection points along that curve.