Difference between MB levels and Gradient Factors

[wetb4igetinthewater]

It appears that Scubapro added their own tweaks to the Buhlmann ZHL-16 algorithm.

Nowadays ZHL-16 is most commonly implemented with Gradient Factors; i.e. is a well-known and understood algorithm that matches across brands of computers if diving with others.

Thus that G2 uses Buhlmann but with proprietary tweaks.

The missing TLAs**:

• PDIS (Profile Dependent Intermediate Stop)
• MB (dunno -- will edit if found out)

**Three Letter Acronyms (including extended TLAs)

One of the advantages of sticking with a dive computer with Buhlmann ZHL-16c + GF is that people understand what the settings that one has, which is kind of a big deal for technical diving. Recreational diving, not as much.

 

[BoltSnap]

6 69

I believe that you mean L6 = 60 not 69

 

[SeanW]

https://www.divetable.info/skripte/G2_GF.pdf

See slide 4
Approximately:
MB L 0 = GFHi 90
1 85
2 80
3 75
4 70
5 65
6 69
It also implies that GFhi=GFlo if using MB levels.

Thank you for this! I see how they compare. I don't use this for technical diving, so I mainly am concerned with exiting GF.

 

[tursiops]

I believe that you mean L6 = 60 not 69

Yes, thanks, edited.

 

[scubadada]

Thanks @tursiops

I had not seen the data regarding MB levels and GFs berfore.

 

[BoltSnap]

https://www.divetable.info/skripte/G2_GF.pdf

See slide 4
Approximately:
MB L 0 = GFHi 90
1 85
2 80
3 75
4 70
5 65
6 60
It also implies that GFhi=GFlo if using MB levels.

It doesn't show the equivalent GF for L7, 8 and 9, does it?

 

[tursiops]

Thanks @tursiops

I had not seen the data regarding MB levels and GFs berfore.

It should be noted that the equivalence is only approximate. If you look at the details in the linked document, (1) the equivalence was done only by looking at TTS (time-to-surface, i.e. the sum of all stops and ascents) for the G2 and for Buhlmann....and (2) there is more than one kind of G2!

 

[rsingler]

https://www.divetable.info/skripte/G2_GF.pdf

See slide 4
Approximately:
MB L 0 = GFHi 90
1 85
2 80
3 75
4 70
5 65
6 60
It also implies that GFhi=GFlo if using MB levels.

I think there may also be a penalty imposed for sawtooth profiles. Several years ago, I found a warning on my computer after a class in which I did three sequential CESA's with students from no more than 25ft. Hardly a decompression risk (though I will no longer do that many in a single dive), but my Luna was unhappy. They may be implementing something undocumented from a bubble model on top of Buhlman. Or perhaps it was just ascent rate. The computer auto-downgraded me from L3 to L0 and added the "microbubble" warning.

 

[ChrisDee]

Hi all!

I was wondering if anyone could explain the difference between MB Levels (found on Scubapro computers) and gradient factors? I have a Scubapro G2 running Buhlman ZHL-16 ADT MB and I'm unsure what the distinction is between the different programmable MB levels (for added conservatism) vs gradient factors (found on computers running non proprietary Buhlman ZHL-16). How do these compare with one another?

Do you have a copy of: Deco for divers / divers guide decompression theory physiology by Mark Powell? I think it is posted somewhere on some site,...or Amazon,.... I found it helpful, but some may say it is dated.

Every time I ask a similar type question Scubapro refers me to page 78 in G2 Manual V1.3 - 06/2021 or this: https://ww2.scubapro.com/en-GB/HKG/heart-rate-monitoring-diving.aspx

I have found that the phrase "Gradient factors" means so many different things to so many different people. Mark Powell's book is a very easy to read book, which is why I suggest starting there,... Apologies if you have already read it,....

It seems your asking how deco is computed between various manufacturers of dive computers, which I suspect is a rather large question. I look in the mirror and each and every time I say this whole subject is a hypothesis, and no one has the final word or can guarantee with certainty any deco calculation. I have seen ascent rates change, times change, the introduction of safety stops, I was a kind of 60 feet for 60 min kind of diver for years,...cause that's all we had, and even then,...that rule didn't always work.

 

[ChrisDee]

I think there may also be a penalty imposed for sawtooth profiles. Several years ago, I found a warning on my computer after a class in which I did three sequential CESA's with students from no more than 25ft. Hardly a decompression risk (though I will no longer do that many in a single dive), but my Luna was unhappy. They may be implementing something undocumented from a bubble model on top of Buhlman. Or perhaps it was just ascent rate. The computer auto-downgraded me from L3 to L0 and added the "microbubble" warning.

Asking as a student,
Does the G2 impose a mandatory safety stop, that in the G2 menu can not be circumvented? In the G2 manual, pages 22, 68, 78 I'm taking all of that to read that the micro bubble display , if you ignore your Level setting, it will "NAG" you by just defaulting to the next less conservative level? As a reminder to not exceed the depth variable ascent speed, that can not be changed either. So if you use a G2, your going to risk gauge mode by not doing the mandatory safety stop, being nagged by a yellow or red speed box, and a warning about the MB level? Could / should we just set the surface interval to less than one minute or just operate the G2 as an instructor in Gauge mode? if we are doing multiple CESAs' can we just set the safety stop timer to "off" ? All of this seems to be related somehow? I mean seriously,...the ins and outs of this G2, we need some kind of more detailed blog, just for the eccentricities of this thing.