Algorithms, Conservative Factors, Altitude, Planned Deco - Questions

[scubadada]

I will bet you a dollar no dive computer manufacturer will ever put in any feature that automatically makes the computer more aggressive (i.e. gives a longer NDL or less deco).

Scubapro has always really bothered me. Take the G2 as an example. They say it runs Buhlmann ZH-L16C ADT MB. What is that deco algorithm, where can you read about it, where can you plan it? There are nearly an endless number of adjustments. You choose a microbubble level of 0-9. You choose to employ profile dependent intermediate stops or not. Then there is workload. You choose to dive the heart rate monitor or not. You certainly do not need to dive with the chest monitor. You can run the breathing rate monitor on any of 25 steps but can not defeat it entirely. You can turn off the skin temperature monitor if you want, even if using the chest strap for heart rate. As per @stuartv, none of these adjustments are going to make your profile more aggressive, only more conservative. The basic Scubapro algorithm, without any adjustments, already appears to be quite conservative, see the 2017 ScubaLab hyperbaric unit tests at Scuba Diving Magazine. Personally, I could not see diving a modern Scubapro computer.

 

[dmaziuk]

I will bet you a dollar no dive computer manufacturer will ever put in any feature that automatically makes the computer more aggressive (i.e. gives a longer NDL or less deco).

Oh, I dunno... depends on where their biometric stuff takes it: it's conceivable that the code may work both ways and it could slip past the legal dept.

PS arguably, Oceanic puts in the "more aggressive" (than PZ+) feature in their offerings.

 

[KenGordon]

As far as carrying double the deco gas, that is because half of it is my buddy's. What you just said means that if my deco requirement is higher AND my buddy loses his deco gas, then one of us is screwed.

Hardly, your plan A would have been the short deco. So if the computer says to switch to plan B (lots of work, warm on the bottom, cold on deco) and your buddies deco regulator dies you are back on plan A - you are no more screwed than if plan B had never existed.

 

[KenGordon]

I don't see how that translates to "figuring out" the impact of biometric stuff. Is there a way for me to run the SP desktop software and tell it to generate a plan based on a heart rate of 150 and a skin temp of 86? If not, that how can I run a plan ahead of time and be confident that the deco it assigns me is the worst case deco requirement?

So, you plan a dive with an RMV of 25/l/minute. You expect to get out with 70 bar, you actually get out with 100. You recalculate your RMV and use that to inform your next dive.

Next you plan a dive with a TTS of 20 minutes. You do the dive and you take 30 minutes. Maybe you were slow at the ascent. Do you a) continue to assume ascents for that dive will take 20 minutes or b) adjust your future planning in the face of experience and budget more gas?

So, now treat the biometric stuff like that. Work out, by diving a few times, what difference is typical and budget gas for that.

If you deeper or longer you eat into your contingency gas. Why not if ou have a high heart rate?

Is there a Scubapro planner?

 

[stuartv]

Scubapro has always really bothered me. Take the G2 as an example. They say it runs Buhlmann ZH-L16C ADT MB. What is that deco algorithm, where can you read about it, where can you plan it? There are nearly an endless number of adjustments. You choose a microbubble level of 0-9.

I have not studied the details on the SP computers. But, if it has a microbubble setting it is NOT just a Buhlmann algorithm.

Oh, I dunno... depends on where their biometric stuff takes it: it's conceivable that the code may work both ways and it could slip past the legal dept.

PS arguably, Oceanic puts in the "more aggressive" (than PZ+) feature in their offerings.

I guess as long as SP keeps their algorithm proprietary and secret, we'll never be able to settle that bet. I will bet you a dollar that no dive computer manufacture will ever admit to having an algorithm that automatically becomes more aggressive.

And nope. There is no (rational) arguing that any Oceanic computer AUTOMATICALLY makes itself more aggressive. You choose before the dive whether to use DSAT or PZ+. Your dive starts with a certain inert gas tissue load and has depth, time, and breathing gas. Whatever those parameters are through the dive, it's going to give you the same NDL or deco. No breathing rate, heart rate, skin temperature or any other variable are going to cause it to automatically give you a different NDL or deco obligation - in either direction, aggressive or conservative.

 

[dmaziuk]

I will bet you a dollar that no dive computer manufacture will ever admit to having an algorithm that automatically becomes more aggressive.

How about "extending dive time under favourable conditions"?

In practice it is ridiculous, of course: if it makes the profile "more conservative" based on the heart rate, than all I need to do is accidentally pull the chest strap wire while "maneuvering through a restriction", and my heart rate and associated conservatism is out of the picture. Considering all the possible state transition the code has to handle in a sane fashion... I'd never buy one of those just from KISS principle.

 

[scubadada]

Oh, I dunno... depends on where their biometric stuff takes it: it's conceivable that the code may work both ways and it could slip past the legal dept.

PS arguably, Oceanic puts in the "more aggressive" (than PZ+) feature in their offerings.

Oceanic computers are pretty easy to deal with. From most to least aggressive, DSAT, PZ+, DSAT with conservatism, PZ+ with conservatism. Gives quite the range from quite aggressive to very conservative. Choose your poison

 

[CandiveOz]

The basic Scubapro algorithm, without any adjustments, already appears to be quite conservative, see the 2017 ScubaLab hyperbaric unit tests at Scuba Diving Magazine.

As part of my investigation, I reviewed the Scubalab results for 2016 and 2017 to determine how conservative each computer really is. Scubalab conducted 4 multilevel dives and recorded the NDL at each depth for each computer. I simply summed these figures on the basis that comparatively lower total NDLs are more conservative. This gave me the ability to rank the computers on each dive as well as provide an overall view. As you can see from my attached table, Scubapro was one of the most conservative computers overall and generally across all dives. The dives profiles were the same each year and Perdix was included both years with different results. This difference may have been due to different GF's selected. See attached PDF.

 

[CandiveOz]

As I said in #26, an approximation by a simplified formula tends to work well enough over a limited range of input values. This "folded" approximation is used in "recreational" computers, it's probably reasonable to assume that it works well enough on no-stop dives to above 60 metres. What does it do if you go deeper and/or longer?

Dmaziuk, thanks for taking the time to post the link to the article you referred to. I couldn't find a date on the document but because it mentioned the Abyss deco program which is no longer developed, I assume it must be early 2000's? My point is, it appears to me that the "folded" RGBM is probably the plain vanilla version we are referring to. Perhaps it was optimised/simplified/folded so it could run on the machines during that time - and could be in use still today.

Point being that Suunto has a pdf showing how EONs behave, but it's not clear that Zoops will behave exactly the same way for, say, longer deco times.

There may not be a pdf available but you do have DM5 to play with to clarify how the Zoops behave.

I think the other question is tunable fudge factors. E.g. would you consider ZHL16-B. ZHL16-C, -B w/ GF 45/70, and -C w/ GF 50/85 "four different flavours" of Buhlmann? Or the same Buhlmann with 4 different "conservatism" settings?

Valid point. Because RGBM is proprietary, we don't know how different the formulas are. But we do know the Buhlmann formula and developers are just changing two variables within the same formula; GFlow/GFhi. But one could argue that changing these variables result in a different Buhlmann formula. I would consider GFhi just a conservative factor. You are getting out of the water at a percentage lower than the model's M value. So 70/70 means you surface at 70 percent. But what about 10/100? This ratio dramatically changes the decompression profile of the model. GFhi is 100 so there is no conservatism. GFlow is 10 so the diver believes deep stops are important. Its a completely different profile to 100/100 (the original formula). I'm sure some programmer could hardcode GFlow to 10 and allow the diver to pick his GFhi and sell this "flavour" as the "Buhlmann deepstop formula - BDF."

 

[KenGordon]

I have not studied the details on the SP computers. But, if it has a microbubble setting it is NOT just a Buhlmann algorithm.

The bubbles are obviously a marketing gimmick. Each setting will be changing the limiting m value a bit, sound familiar?

Valid point. Because RGBM is proprietary, we don't know how different the formulas are. But we do know the Buhlmann formula and developers are just changing two variables within the same formula; GFlow/GFhi. But one could argue that changing these variables result in a different Buhlmann formula. I would consider GFhi just a conservative factor. You are getting out of the water at a percentage lower than the model's M value. So 70/70 means you surface at 70 percent. But what about 10/100? This ratio dramatically changes the decompression profile of the model. GFhi is 100 so there is no conservatism. GFlow is 10 so the diver believes deep stops are important. Its a completely different profile to 100/100 (the original formula). I'm sure some programmer could hardcode GFlow to 10 and allow the diver to pick his GFhi and sell this "flavour" as the "Buhlmann deepstop formula - BDF

All these computers (ScubaPro and GF) are equally NOT Buhlmann. If could easily be that GF is further away from actual ZHL16 coefficients than the ScubaPro one.

This point from CandiveOZ is true, the whole idea of GF was to fake up bubble model profiles with simple disolved gas planners. The computer manufactures followed the fashion by adding deep stops, either Pyle style (like the Helo2 and maybe this ScubaPro), by GF (30/70 anyone?), VPM or otherwise (Eon etc).

Now that the deep stop fashion has been debunked user since are left turning these off, either explicitly, by choosing GF values that don’t do that (no all options are typically available though) or ignoring them.