Bühlmann vs. RGBM
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Right, but there are some things I didn’t get:
- If the Bubble models are really that bad, why are gradient factors like 30/70 used to mimic them still ( see Mitchell)
- Suunto reacted with the fused RGBM (2), which looks very different in the dive profile in DM5
- The big problem is the deep stop. Its optional and I deactivated it
So is all the said still true today? Or was it too late and nobody trusted something with Bubble in the name anymore?
If it really would be 100% sure that Buhlmann was correct everyone would dive with GF 100/100…
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The problem is that decompression theory is nothing that can be exactly calculated. Everything is based on models tuned to data obtained via more or less trial-and-error studies. There is no model which can define an exact threshold from which on you get DCS symptoms and since there are so many unknowns and relevant factors there most likely never will be.
Buhlmann developed a model capable of defining a threshold which gives you a fair chance of not developing DCS symptoms if you don’t cross it and the question every diver needs to ask themselves is whether this chance is acceptable for them or not. If they accept the chance they use GF 100/100 but if they say the chance is too high for them, they go with GF 30/70 or something else. In that sense the model is neigther correct nor wrong, but experience shows it’s working.
I think the fact that Bubble models are dying out is because Buhlmann has become a de-facto standard in the industry and when diving together it makes sense for everyone to use the same algorithm so that they can easier synchronize their NDL or Deco times.
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@Triple-S You have a point here regarding the possibility to “synchronize” algorithms based on the GFs for a group. This is something thats not possible for RGBM
Regarding the 30/70 I think this isn’t State of the Art anymore. Also not 40/85 like default on the Ocean. If you really believe in the Buhlmann theory something like 100/85 would be best to avoid saturation during the first stop. But again that doesn’t seem to be possible on the most dive computers -
Many, not all, who’s doing deep, helium, diving today use
GF Low 50
GF High 70-85Some even change the GF:s during deco depending on conditions.
GF Low 50 will get you away from the deep ie eliminate deep stops.
Why are you interested in RGBM and not (the salvation of all divers) VPM?
What about GAP or DCIEM?
Interesting but not connected to this is the report from DAN regarding risks of sickness
https://youtu.be/OnorWqH9Zs4?si=Ebofmi2haEqLmwbJ -
@ccrhenrik Thank you for the insights! I’m interested in RGBM in special because I recently got a Suunto Eon Core and now have the option to choose between Fused RGBM 2 and Bühlman ZHL-16. Before I had Sunnto Zoop and Mares Smart Air, so always RGBM.
Hard decision. For No-Deco dives its just a little different NDL time for first and repetition dive. But I plan to try deco, so I want to know more about the options
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@VoiGAS
One of the problems with RGBM is that it is proprietary. No-one but it’s makers know what’s happening in the background. No-one can see or audit the workings of the algorithm.Here’s an old video with one of the makers “selling in” the Fused RGBM https://youtu.be/QuawWoqp87k?si=ikIhSnq-Thu6kyj6
He, as a developer of RGBM, gives a comparison with Bühlman here https://youtu.be/6OoDqfuQ1Lo?si=aXnt1hq0GALBfH8r
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I think now I know why Suunto chose GF40/85. Its virtually the same like the Fused RGBM, at least for this sample 50m for 15 minutes deco dive.So I guess I am quite safe no matter which one I choose
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@ccrhenrik True, thats a negative aspect. And if Buhlmann with 40/85 is similar in stops it also should reduce bubble formation like RGBM.
Good to have the choice -
V VoiGAS referenced this topic
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@VoiGAS, I purchased the Nautic end of Dec 2025 when it became available in Netherlands. Due to the fact that I missed the flexibility which my Suunto EON had to dive with two algorithms (RGBM & Buhlmann), I was comparing the Nautic Bulmann table vs RGBM because my buddies were using RGBM on their EON’s and Vypers.
My old computer was the EON Core and I used them on the same POD in my dives to do the comparison.
Let me be clear, I am a recreational diver with a good level of experience and I’m diving mainly in Netherlands, I do single dives on Sunday mornings so I didn’t compare situations like repetative diving and situations where RGBM locks out for omitting deco stops and Buhlmann takes this into account for next dives.
I mainly was interested to have a comperable setting on the Nautic which was close to the RGBM P0 setting. We had some deep dives planned and we needed to have all computers reach Deco -1 at +/- the same time as this indicated the start of our ascent to the surface.
The RGBM Default value P0 was less conservative then the Buhlmann default value - 40/85 (Medium) so for the next dive I changed the Nautic to the 45/95 (Low) value. This seemed to work quite wel and yes behaviour of the buhlmann is a bit different but in general this setting matched RGBM P0.
I’m confident that the RGBM P0 which I dived on my Cobra’s, Vypers and EON’s was matching 45/95. So this is the setting on my Nautic I am using until today. My EON core remains as backup on P0.
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@hhouter I also thought about a similiar GF value because RGBM always served me well. What I don’t like is the Lockout - it seems dangerous to me to disable the computer during the dive
Thats something that doesn’t happen with Bühlmann, right? -
@VoiGAS Correct, but it doesn’t lock you out during the dive. It locks the computer for successive dives after you have omitted the mandatory stop which is not common practice anyway…
. In these rare situations RGBM locks the computer for 48 hours. You can dive with it but not as a computer.See this link: https://www.suunto.com/en-gr/Support/Product-support/suunto_eon_core/suunto_eon_core/features/ceiling-broken/
But Buhlmann doesn’t. In principle it corrects / penalizes you for next dives. So locking out is not what the Buhlmann implementation in the Suunto does. Every other brand might do it in a different way.
In general you can assume Suunto RGBM is less conservative for single dives and P0 (Default) can be perfectly aligned with the 45/95 GF (Low setting in the Nautic menu).
Buhlmann is less conservative in multiple / successive dive scenarios and allows detailed tweaking based upon the personal preference where RGBM only has the five P settings. I personally didn’t compare these situations as I do single dives only. But having both tables as in the EON’s would have been my preference, although I understand that you never switch when the option is there. I also understand it from the maintenance and support perspective Suunto made this choice introducing it in the EON (Both) to standardizing on Buhlmann in the Ocean and Nautic’s for new generation devices.
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@hhouter Great insights, thank you! I think the Mares locked during the dive - definitely something I don’t want.
So I can stay with RBGM and if I want to switch the option is here to do it with similar behaviorEdit: But in the Link you provided the screenshot shows a Locked screen while on 5m depth - could it be that it was just the 3 minute delay that allowed you to surface?
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@VoiGAS for the EON, thats correct as they hold both tables. You can switch over or set Buhlmann as default where locks do not occur. But this does not downplay the fact that the ceiling was not followed and decompression was not finalized. This will have impact on further calculations as Buhllman uses its nitrogen buildup for further calculations. So better not to have these sitiations and allways follow the indicators on the computer to the letter.
Suunto does make the difference between voluntary or mandatory decompression stops. The RGBM lock only applies to the latter.
The screen showed in the link indicates a mandatory situation which is explained by Suunto… you get a warning to go to the ceiling of 6,5 meter. You need to do that within 3 minutes and sit out the deco as long as indicated by the EON, in this case 75 minutes which is far from beeing recreational…
If you fail - after warnings like the red ceiling indication and audible signal - to comply within 3 minutes, the computer locks for 48 hours. So you might say it indeed locks during the end of the dive.
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