Bühlmann vs. RGBM

ccrhenrik

Many, not all, who’s doing deep, helium, diving today use

GF Low 50
GF High 70-85

Some 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

VoiGAS

@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

ccrhenrik

@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

VoiGAS

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

VoiGAS

@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

hhouter

@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.

VoiGAS

@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?

hhouter

@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.

VoiGAS

@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 behavior

Edit: 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?

hhouter

@VoiGAS for the EON, thats correct as they hold both tables. And after a lock of RGBM you can switch over to Buhlmann and continue with care as the computer doesn’t lock for the purpose of locking but saving yourself to avoid getting DCS.

The screen showed in the link indicates a situation which is explained by Suunto… you get a warning to go to the clieling of 6,5 meter. You need to do that within 3 minutes and sit out the deco as long as indicated by the EON.

If you fail after red clieling indication and audible signal, to comply within 3 minutez, the computer locks for 48 hours. So you might say it indeed locks during the end of the dive.