Dive Computer Brawl

[DeWayne]

Without knowing exactly what figures they've got in the algorythm, there's no way to know exactly what it produces, or if it can be reproduced with a table generator. If I can cut tables with VPlanner, and the VPM model they're using offers some form of 'tweaking' to get added conservatism if I'm not happy with the original, then it might be ok.

I still haven't gotten any response back whatsoever to my query to Delta-P on all of this however....

The beauty of VPM-B is that it shouldn't require tweaks (at least in theory).

I will ask Kevin some more questions. Hopefully, I will be able to get the answers for you.

Ask him if they are close to having a date set for implementation. It will be very interesting to see what is finally released.

[DeWayne]

I've researched the math behind both VPM and RGBM beofre deciding which to trust. The mathematical modeling in VPM is much cleaner and progressive while Bruce relies on older analysis models, which is indeed typical for most physicists. I have found small glitches in RGBM, true it would take a lot of deco time for them to ever make their pressence known, but they are there. Have yet to be able to make the VPM model fail that way. My background btw is in theorectical mathematics, noncommutative algebras and quantum groups.

Wienke, B.R., Decompression Theory (ftp://decompression.org/pub/Wienke/ file named deco.pdf, pages 76 - 77):

“The RBGM has its roots in the earlier work of the Tiny Bubble Group at the University of Hawaii, drawing upon the so-called Varying Permeability Model (VPM) to multidiving, altitude, and mixed gas applications. While certainly not radical, the RBGM is both different and new on the diving scene. And not unexpectedly, the RBGM recovers the Haldane approach to decompression modeling in the limit of relatively safe (tolerably little) separated phase, with tolerably little a qualitative statement here.

The Suunto VYPER is an RBGM-based decometer for recreational diving (plus nitrox), while ABYSS/RBGM is a licensed Abysmal Diving software product. On the Internet, the sites http://www.suunto.fi/diving.index.html and http://www.abysnal.com/index.html can be visited for information and description. Both are first-time-ever commercial products with realistic implementation of a diving phase algorithm across a wide spectrum of exposure extremes. And both accommodate user knobs for additional conservatism.

Here, our intent is to (just) look at the underpinnings of both meter and diveware implementations of the RBGM algorithm, one with extended range of applicability based on simple dual phase principles. Haldane approaches have dominated decompression algorithms for a very long time, and the RBGM has been long in coming on the commercial scene. With recent technical diving interest in deep stop modeling, and concerns with repetitive diving in the recreational community, phase modeling is timely and pertinent. And, of course, since the RBGM extends the VPM, much of the following applies to the VPM directly.”

I corresponded with Bruce while I was looking into both models. From a practical application point of view what he has is great. From an anal mathematician's point of view, I found the VPM model to be cleaner and easier to work with and less prone to failures. Keep in mind that the runs I did to produce a failure far excede what any human would ever be capable of, and were infact quite minor at that point. Both have been great as a platform for looking at an even more inclusive model that perhaps one day I will be able to work the kinks out of.

[OFG-1]

Man, am I sorry that I asked this question. I have decided to construct my own computer. I am sealing a small cat inside a 1 gallon Mason jar, hooking up a second stage to the lid so the cat is in ambient pressure, and breathing the same gas that I am. Then as I ascend, when the cat starts to look really uncomfortable, I will stop until it calms down. Plans for this computer will be available on PETA's website under the extreme cruelty to animals section by late next month. I refer to this as the T.V. algorithim (Tender Vittles). Naturally, if you are not careful during the dive, and break the "lens", you would have a cat-a-strophic computer failure. Ther only real design issue left is how to get a litter box in the jar.
Cat Diapers. Thet's the answer.

[Genesis]

The scary part of the cite you provided above from BRW's paper is that its not actually true.

The Vyper is NOT a true RGBM meter, nor is any other Suunto. They all run a Buhlmann/Haldane-style algorythm with a "folded" RGBM piece of code on top of them. NONE of them produce deep decompression stops.; indeed, all show ceilings that, if followed, produce a straight Buhlmann/Haldane-style decompression curve! The decompression ceilings they display produce profiles that are wildly at odds with the current thinking regarding deco. Near as I can tell (Suunto won't disclose specifics) the ONLY influence the "RGBM" stuff has in there is to produce reduced no-stop times for repetitive diving.

You CAN dive them with a modern decompression curve, but YOU have to do it manually - the computer sure won't. I own three of Suunto's products, by the way.... and have a LOT of dives on them - I know exactly what kind of decompression "suggestions" they produce.

This is what I call "math meets marketing", or, to perhaps be a bit rude, "math meets money." More to the point, it entirely removed my interest in RGBM; I expect straight answers to questions when it comes to software like this - and this sort of statement is IMHO a credibility-destroyer.

The scary part of the cite you provided above from BRW's paper is that its not actually true.

The Vyper is NOT a true RGBM meter, nor is any other Suunto. They all run a Buhlmann/Haldane-style algorythm with a "folded" RGBM piece of code on top of them. NONE of them produce deep decompression stops.; indeed, all show ceilings that, if followed, produce a straight Buhlmann/Haldane-style decompression curve! The decompression ceilings they display produce profiles that are wildly at odds with the current thinking regarding deco. Near as I can tell (Suunto won't disclose specifics) the ONLY influence the "RGBM" stuff has in there is to produce reduced no-stop times for repetitive diving.

You CAN dive them with a modern decompression curve, but YOU have to do it manually - the computer sure won't. I own three of Suunto's products, by the way.... and have a LOT of dives on them - I know exactly what kind of decompression "suggestions" they produce.

This is what I call "math meets marketing", or, to perhaps be a bit rude, "math meets money." More to the point, it entirely removed my interest in RGBM;

My comment was in regards to Dewayne’s statement about RBGM. I thought about leaving out the paragraph about the Suunto and Abyss computers, but I left it in. Both web links don't work and the Suunto is a modification of RBGM (Suunto RBGM).

I expect straight answers to questions when it comes to software like this - and this sort of statement is IMHO a credibility-destroyer.

I'm only trying to help here! I posted some of what was written on RBGM and I'm sorry if you didn't like it.

[crazyduck]

Man, am I sorry that I asked this question. I have decided to construct my own computer. I am sealing a small cat inside a 1 gallon Mason jar, hooking up a second stage to the lid so the cat is in ambient pressure, and breathing the same gas that I am. Then as I ascend, when the cat starts to look really uncomfortable, I will stop until it calms down. Plans for this computer will be available on PETA's website under the extreme cruelty to animals section by late next month. I refer to this as the T.V. algorithim (Tender Vittles). Naturally, if you are not careful during the dive, and break the "lens", you would have a cat-a-strophic computer failure. Ther only real design issue left is how to get a litter box in the jar.
Cat Diapers. Thet's the answer.

This is the damn funniest thing I have read in months!

YOu need to send this to Overhead TImes under the Humor Section.

OH MY GOD! Here is your sign.

PS- someone needs to add an alert warning. I sprayed my keyboard and I am not a CAT.

Andrew

[crazyduck]

I expect straight answers to questions when it comes to software like this - and this sort of statement is IMHO a credibility-destroyer.

I seriously hope that you are referring to distribution channels and manufactures and not all of the hard work that Chip has done by bringing this all together. A little clarification here would be a good thing!

For those of us that have been battling with manufactures over the release of information, this has been a great thread. I wish that we could bind this kind of material and hand it out to friends who are buying new dive computer. Some people have no idea all of the things that go into these little jewels.

Andrew

[Genesis]

I understand Chip, and please be aware that I'm NOT in any way attacking you or what you're doing here, but to me, at least (and I hope to others!) marketing hype is a major problem when it comes to stuff like this.

After all, we're expected to trust that these implementations won't turn us into pretzels. Its just a wee bit more important than most of the other marketing hype out there...

I understand what you were doing, but in doing so you illustrated one of the problems in the industry when it comes to meters and software - its not exclusive to RGBM, but this just happens to be one of the screaming examples of hype over substance.

RGBM in general is one of the wildest examples of this. Find the various meters and programs out there that claim to be "RGBM", plug in a given dive, and note something nasty - they all spit out different profiles. Which one is "true" RGBM? Who knows! This is the general problem with not knowing where the "knobs" are set, and there being no proclaimed "correct" place to twist them to point.

I'd LOVE to find just ONE meter intended for technical diving where its ALL laid on the table, where the deviations from the model's designer are documented, and where you can twiddle them back to the designer's intended settings (or to other settings as the designer changes his/her mind - or mathematics!) change.

The VR3 is uniquely suited to this possibility, since it CAN be reprogrammed. Delta-P has not seen fit to make it possible to do without returning to them (perhaps for liabiltiy reasons, or perhaps for business reasons) but the capability, when the VR3 was first announced, excited me - simply because for the first time "its all hardcoded" was no longer true.

Sadly, its turned out not to matter much in reality, which is a bummer. I was hoping that the VR3 would make use of its IR interface capability to make possible flash updates, much like we do with a PC BIOS.

[Rick Palm]

If you deep dive, my Duo is off on depth. On a recent deep dive, my Duo read 318 feet, which was off by about 40 feet. For shallower cave dives, it seems fine, and I like the big letters. It's good for cave dives requiring just two mixes, fine for most of my diving.

[Al]

I'd LOVE to find just ONE meter intended for technical diving where its ALL laid on the table, where the deviations from the model's designer are documented, and where you can twiddle them back to the designer's intended settings (or to other settings as the designer changes his/her mind - or mathematics!) change.

How about your brain? Models are models, and none of it is real. Follow a well tested model until you know what you're doing, then do what you know. Dive computers will always be BS, because behind each one is a company that can be sued.