Difference between MB levels and Gradient Factors

[Sevenrider860]

Could you post the studies that show this is beneficial? I have done a lot of research on this topic, and I seem to have missed them.

What are you wanting me to show is beneficial? Do you feel that having the additional information at what depth you start off-gassing versus on-gassing serves no purpose? It is just information. Use it or don't use it. Have you asked Shearwater to shows studies that show the GF99 function is beneficial? MultiDeco shows the off-gassing depth in your dive plan. Have you asked Ross to post studies to show that providing that information is beneficial? Again, it is just information available. You can turn off PDIS if you don't want to see your off-gassing depth...it is pretty simple.

If you took from my comments that I am stating that performing the 2 minutes stops at the depth shown by PDIS is beneficial, then you misunderstand.

 

[Sevenrider860]

Which you're saying is a good thing?

Or to put it another way, why do you need to tie an expensive brick to your wrist?

There's a good reason why Shearwater computers are popular with most rebreather manufacturers and technical divers. And it's not because they become part time bricks (or have some made-up proprietary algorithm).


Because it was running a different deco curve than the plan called for. So it goes into a massive sulk like some sullen teenager.


Nor a computer that bricks itself on the surface for a 2 day arse covering sulk.

I don't think I ever said it is a good thing, but I don't think that is the end of the world for most recreational divers either.

Rebreather and technical divers are a small percentage of divers buying computers...I will be the first to say that the G2 is not the computer they want. I don't see anybody (ok, I don't see any sensible person!) trying to convince CCR and technical divers to drop their Shearwaters and replace them with a G2 either. For non-ccr and non-technical divers, proprietary algorithms based on Buhlman or RGBM are not using the "devil's" algorithm like some people make them out to be. For a recreational diver, the G2 is a nice computer and is cheaper than the Shearwater here in the USA. G2 + Transmitter = $1,350. Perdix 3 with Swift Transmitter = $1,475.

The G2 Tek which is running ZHL-16 GF is not a bad technical dive computer either. I use it as a backup to my Shearwater Petrel 3 when on CCR. I am able to keep some of my checklists on the G2 Tek. It tracks the primary controller just about as good as the Perdix 2.

 

[boulderjohn]

What are you wanting me to show is beneficial? Do you feel that having the additional information at what depth you start off-gassing versus on-gassing serves no purpose? It is just information. Use it or don't use it. Have you asked Shearwater to shows studies that show the GF99 function is beneficial? MultiDeco shows the off-gassing depth in your dive plan. Have you asked Ross to post studies to show that providing that information is beneficial? Again, it is just information available. You can turn off PDIS if you don't want to see your off-gassing depth...it is pretty simple.

If you took from my comments that I am stating that performing the 2 minutes stops at the depth shown by PDIS is beneficial, then you misunderstand.

I wanted to see the studies showing that doing a stop at that depth is beneficial relative to simply ascending to a safety stop.

 

[Sevenrider860]

I wanted to see the studies showing that doing a stop at that depth is beneficial relative to simply ascending to a safety stop.

John, I never made that statement. I know you do not have comprehension issues. Where in my comments am I stating to perform a stop at depth? I am stating that enabling the PDIS feature provides you a display of the depth where you will switch from on-gassing to off-gassing.

"While Scubapro markets PDIS as a 2 minute intermediate "stop", it did not have to be used that way."

"You never had to make the stop and you were never penalized for not taking the stop, but it allowed a quick view of what your on-gassing/off-gassing depth was."

 

[boulderjohn]

John, I never made that statement. I know you do not have comprehension issues. Where in my comments am I stating to perform a stop at depth? I am stating that enabling the PDIS feature provides you a display of the depth where you will switch from on-gassing to off-gassing.

"While Scubapro markets PDIS as a 2 minute intermediate "stop", it did not have to be used that way."

"You never had to make the stop and you were never penalized for not taking the stop, but it allowed a quick view of what your on-gassing/off-gassing depth was."

What I am saying is that people are hyping features of a computer, including this feature, that have been added to that computer with no evidence that they do any good and which may, in fact, do harm.

 

[L13]

John, I never made that statement. I know you do not have comprehension issues. Where in my comments am I stating to perform a stop at depth? I am stating that enabling the PDIS feature provides you a display of the depth where you will switch from on-gassing to off-gassing.

"While Scubapro markets PDIS as a 2 minute intermediate "stop", it did not have to be used that way."

"You never had to make the stop and you were never penalized for not taking the stop, but it allowed a quick view of what your on-gassing/off-gassing depth was."

As an informational feature this sound nice. Any (reasonably short) stops above this depth should not add significantly to the already required deco, where as stops below this would.

 

[tursiops]

As an informational feature this sound nice. Any (reasonably short) stops above this depth should not add significantly to the already required deco, where as stops below this would.

So we have a computer that even its advocates say is best for NDL diving, and we are arguing about aspects of its behavior on deco diving? OK.

 

[boulderjohn]

Here is a far-flung analogy to explain my last point.

Years ago, I was working in a high school that, like most high schools, was perplexed by the percentage of students habitually failing classes. One teacher was listening to students talking about their part time jobs, and he decided that the students were working way too many hours, and he theorized that we could help our failure problem significantly by finding a way to limit the number of hours students worked during the school year. Everyone was enthused with the idea. I was tasked with dong the preliminary research of surveying student work schedules and correlating them with grades. To everyone's shock, the results were the precise opposite of what was expected--in general, the more hours a student worked, the higher the grade point average. The students who were habitually failing were pretty much not working outside of school.

When Wienke and Yount promoted their algorithms (RGBM and VPM) years ago, they pushed the theories hard, and almost everyone bought into it. I did. They had no research supporting those theories, but everyone was sure that was just a matter of time. It wasn't. No research has supported their approaches on decompression dives, and they are now no longer in favor.

No one doubts that there are more factors involved in decompression that are included in current algorithms. It's just that no one really knows enough about how they are involved to make any definitive statements. As such, I am leery of any computer algorithm that includes factors that adjust the approaches that have been studied for more than a century without some indication that those adjustments actually help.

 

[L13]

So we have a computer that even its advocates say is best for NDL diving, and we are arguing about aspects of its behavior on deco diving? OK.

Who is arguing? Not me. Over all, I'm not a fan of a proprietary algorithm/research or bricky DC's. But I also have no personal experience with the G2, so not participating in the argument.

I was just noting a nice feature. Even in NDL it could be informative, above the depth NDL time available should start increasing. Below it, NDL time would continue to decrease.

 

[L13]

No one doubts that there are more factors involved in decompression that are included in current algorithms. It's just that no one really knows enough about how they are involved to make any definitive statements. As such, I am leery of any computer algorithm that includes factors that adjust the approaches that have been studied for more than a century without some indication that those adjustments actually help.

Very true.

But not really relevant to @Sevenrider860 's suggestion of using the PDIS feature for informational purposes. The depth at which it occurs is directly relevant to the ZHL-16C with GF's algorithm (if it works as he described), much as GFsurf is useful information-ally even though no separate research (that I know of) has been done on it (it's usefulness is implicit from understanding the base algorithm).