Algorithms, Conservative Factors, Altitude, Planned Deco - Questions

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CandiveOz

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If any of my assumptions below are inaccurate, please correct me.

First, let me provide you with some background. I am a recreational diver and have never conducted decompression dives. I may train to deco dive in the future. My current Dive Computer (DC) is a Tusa IQ750 which employs the Pelagic Z+ (PZ+) algorithm. The computer has one conservative factor (CF). If turned on, the algorithm shortens the No Decompression Limit (NDL) based on a higher altitude. At sea level, the calculations are based on NDLs listed for the 5,001 – 6,000 foot range. The computer automatically adjusts for altitude (no manual adjustment necessary). If diving at an altitude higher than sea level with CF turned on, the allowable dive times are calculated based on the next higher 3,000 foot altitude. This CF method is logical and simple to understand and user documentation lists all the different NDLs for each altitude range. Unfortunately I can’t find any software program which uses the Pelagic Z+ algorithm to generate a planned decompression profile. My computer will only show the maximum NDL per depth based on my current nitrogen load. Now, I may not conduct decompression dives myself, but I still want to play with the algorithm before a dive to determine my deco obligation under “what if” scenarios which may result in a short deco stage.

I don’t have any experience with any other type of computer, but I am considering an upgrade and have downloaded the user manuals for those computers I am interested in, read reviews on this forum and other websites and watched youtube videos on these computers. While the computers may be different in terms of form factor, air integration and tech configuration, I am going to focus on algorithms, conservative factors, altitude adjustment and deco dive planning.

I’ve been able to lump the computers into 4 groups;

Tusa, Aqualung, Oceanic – all are basically the same, using the above CF method. The only real difference is Oceanic which includes the DSAT algorithm in addition to PZ+. As mentioned above, these computers automatically adjust for altitude but no deco dive plan profiles can be generated on desktop software or within the computer itself. Dive planning within the computer is limited to NDL per planned depth.

Suunto, Mares – use the Reduced Gradient Bubble Model (RGBM). Mares and Suunto may not use the exact same RGBM but a variant of the model. They both offer CFs and manual adjustment for altitude. In terms of planning deco dives, Suunto desktop software offers this functionality, while Mares display deco obligations of depth and time in the dive computer itself. So while RGBM is proprietary and not open source, both companies allow the diver to plan decompression dives if required. A caveat with RGBM; because it is proprietary and takes into consideration and adjusts for multiday, repetitive diving, previous deeper dives and accent rates etc, a tech diver may be reluctant to use this algorithm because it may change the deco obligation during the dive itself which wasn’t planned for in terms of gas reserve.

Scubapro – depending on the DC model; Buhlmann ZH-L8 or ZHL-16 which can be altered if skin temperature and heart rate are taken into consideration to estimate workload during the dive. Scubapro offers 9 CF’s called microbubble (MB) levels. Altitude is adjusted automatically and deco dive planning is conducted within the computer itself rather than on a desk top computer. Because of these additional “in water” variables, I assume a tech diver would have a difficult time planning a decompression dive with this computer. Another unique feature with the Scubapro and unlike the other computers listed, the nine microbubble levels are “soft” conservative factors. If, for example, MB level 9 is chosen at the start of a dive, and it is breached during the dive, rather than a violation, the computer drops to MB level 8. The computer will continue to drop levels until MB 0 (zero). Then the diver is obligated to follow protocol or be in a “hard violation” and locked out. Therefore, with the Scubapro, you are allowed to set a high conservative factor but can breach it without consequence. But I’m not sure if this applies to the heart rate/ skin temperature chest monitor. In my opinion, the chest strap is a “hard” conservative factor. Based on its readings, the computer may end a dive earlier than planned. As a runner I use a Garmin heart rate GPS watch on all my runs so I like what Scubapro has initiated. But I also know that on my run, sometimes my chest strap doesn’t send a signal and I have to wiggle it to get it going or there is a spike in the heart rate reading for whatever reason and another wiggle to correct the reading. These data anomalies are not a problem on a run, but what happens on a scuba dive?

Shearwater, OSTC – uses Gradient Factors (GF). They too can auto-adjust altitude so no manual adjustment is necessary. The great feature of the Shearwater and similar computers using GF’s is the ability to apply any conservative factor by changing the GF’s. This is the most flexible in terms of user adjustment. Also, for an additional cost, VPM-B can be installed and it has 0 to +5 conservative settings. Again, once you understand how Gradient Factors work, the methodology is logical. There are a number of computer programs can be used to profile deco dives based on these algorithms so nothing is hidden in a black box.

Finally, here are my questions to the forum members who use one or more of these specific DC groups.

Tusa, Aqualung, Oceanic users –
  1. Does anyone use these computers for deco dives? If so how do you plan the dives? Estimating gradient factors for PZ+ I guess is a possibility and GFhi could be estimated based on the published NDLs but how would you approximate GFlo unless you actually took the computer on a deco dive?

Suunto, Mares users –
  1. How are the conservative factors established? How conservative are they? Are they related to or equivalent to the altitude settings?
  2. These computers allow altitude to be manually set. So does this not broaden the computer’s conservative factor range? For example say your computer had CF 0, 1, 2. And altitude setting (AS) 0, 1, 2, 3. Theoretically you have 12 conservative settings with the most conservative as CF2/AS3.

Scubapro users –
  1. What has your experience been with the heart rate monitor? Do you use it?
  2. Have you ever had large heart rate spikes during a dive? What was the consequence?
  3. What factors do you take into consideration when setting a MB level. Do you set a microbubble level and keep within its limit or do you breach its limit occasionally or all the time?
  4. Is there a way of telling when the computer applies a conservative factor based on the reading from the chest strap? Does the computer use the microbubble level to employ this adjustment? Say for example you enter the water with an MB 3 but when you finish your dive the MB level was 5. And the reason for this was the computer estimated your workload during the dive as high and pushed up the conservative factor/MB level. Is that how it works?

Shearwater, OSTC users –
I don’t really have a specific question regarding these computers since they seem to be addressing the needs of both recreational and technical divers. Certainly if you are spending $1,000 - $1,500 on a dive computer, you have to take these instruments into consideration. I suppose my question is what is the next step?

Simplicity is a good thing; particularly with deep/tech diving which is difficult in itself. And being able to adjust gradient factors we can take into consideration cold water, higher workload, age etc. Divers probably start with one of the gradient factors suggested by Shearwater and then through experience fine tune their GF. But is this self assessment enough? Are we biased on our own personal fitness and ability? A 60 year old diver, with a BMI of 32 and high blood pressure is not the same as a 24 year old diver with a BMI of 22 and normal blood pressure. Can we objectively take into consideration age, lifestyle and fitness to dive to establish a personal, custom conservative factor or gradient factor. And can we overlay that with real time monitoring so that actual workload can be taken into consideration? And to make this all work, dive planning would take into consideration these precondition factors along with a worst case real time event and basically generate a plan based on the high risk diver in the group or “the weak link in the chain.” Is Scubapro on the right track but their implementation has to be more transparent so that divers can fully understand, appreciate and accept the model being employed. Is this an opportunity for other manufacturers to use the same technology and offer it as an option for divers to incorporate. I can naturally see Garmin and Suunto going down this track since they already employ heart rate monitors with their GPS watches. But the key to success is not a proprietary black box but openness and transparency – something that Shearwarter and others capitalised on along with robust hardware and great customer service. What is the future for decompression models and dive computers?
 
Far and away the most recommended computers on ScubaBoard are Shearwaters. If you are looking for a mixed gas computer, to me, it’s a no/brainer and there are several threads that go into the reasons why. Keep in mind you can also purchased a used Shearwater for a relatively good chunk less than retail; with all of the new SW entrants in the market there is actually a decent used shearwater market out there now, whereas there did not used to be (bc everyone kept theirs bc they loved them).

If you are looking for a Nitrox computer, there are some decent puck options out there for less than $200 new.
 
PS - in terms of planning dives, not many people use their computers to actually plan the dive. It’s much easier to spend $10 and purchase a smartphone app like Baltic for planning. With the proprietary algorithms, I guess one may HAVE to use the computer for planning; if so, that is one of the downsides.
 
Hi lv2dive,
Thanks for the feedback. Yes, if I wanted to buy a brand new computer, Shearwater would be the choice but as you know its a buyers market when it comes to used dive equipment and if you are patient, you can usually pick up a pretty good kit for less than half the price. Unfortunately here in Australia, the secondary market for Shearwaters is currently nonexistent and will be that way for a number of years. I suspect Aussie divers are now transitioning to Shearwater and offloading their current gear. If you can post a link to the secondary market you referred to I would be interested in seeing what they are going for.

Hence this is the reason why I am interested in the other groups of computers and would like forum members to answer my specific questions. These other computers do have their advantages. For example, if I purchased a Aqualung/Oceanic with wireless air integration, when I eventually upgrade to a Shearwater, I can still use the same transmitter. I'm also familiar with the PZ+ algorithm they employ and I can trial DSAT if I get an Oceanic. The Suuntos and Mares do have depth in the secondary market here and it would be easy to pick up an air integrated unit. RGBM may be conservative, but for a guy who already spent time in the Townsville hyperbaric chamber due to a hit, I welcome conservatism. Likewise, the Scubapro is an interesting option. Every other day I use a heart rate monitor in my training so I appreciate the logging of this data. Therefore I am interested in divers who use Scubapro. How material is the change in the dive profile based on the biofeedback? And as for the Shearwaters, what's on the agenda? I doubt if anyone really knows the answer to this question unless you work for the company but its nice to speculate.

Lv2dive, thanks again for your comments and recommendation. :)
 
Up until very recently, there has been a very limited market EVERYWHERE for preciously-owned SW products. With the introduction of some new options, the second-hand market has only recently opened up.

I meant market in a general sense - SWs can be found on ScubaBoard, Craig’s List, Facebook, etc. sorry for the confusion.

Good luck finding the right solution!
 
I've been diving an Oceanic Atom since I started diving (4 years ago). I have done all my technical diving using Shearwater. Some with a Seabear H3 as backup. One technical dive with my Atom as backup.

Never say never, but I would never do a technical dive with an Oceanic as my primary - UNLESS it was a case of planning the dive using something like Subsurface and then doing the dive with a written deco plan and using the Oceanic in gauge mode. But, since I would NEVER do a technical dive with only one computer, and my Oceanic is my backup-of-last-resort (for tech dives), I feel pretty safe in saying I would just never use it as my primary on a tech dive.

My Seabear crapped out on the first day of a recent trip, so I used my Oceanic as backup to my Perdix for the rest of that trip. I did one actual deco dive on that trip and carried a written plan in wet notes to use with my Oceanic for in case my Perdix crapped out.

I am 100% in the wireless AI camp. I use it for all my diving. I have dived with a physical SPG in 2 or more years. I generally carry a spare transmitter with me on trips. I now have 3 computers that work with those transmitters (Atom, Perdix AI, and Teric). Thus, as you'd guess, I definitely think it's a good idea, IF you want AI, to buy a computer that works with what has become the ubiquitous transmitter - i.e. the PPS one that works with Shearwater, Oceanic, Aqualung, etc..

What I have been doing is, for non-technical dives, dive with my Atom and Seabear (which was a non-AI) computer. The Atom would give me tank pressures and a very liberal NDL. The Seabear would give me a more conservative ascent, should I choose to follow that. Now that my Seabear has died and been replaced with a Teric, the Teric will be my main computer for all open circuit diving, with either the Atom or the Perdix as backup, just depending on the dive. Warm, clear water with good viz, I'll use the Atom. Low viz, I'll use the Perdix.

Personally, with the market being what it is today, I would not buy a new computer that doesn't work with the PPS transmitter. But, that is based on MY whole hog embrace of AI. And that is as applied to buying a NEW computer. Because of Shearwater, the market now has a decent number of decent used computers available that are non-AI or that don't work with the PPS transmitter. If having AI is not important to you, then a good, used computer of most any reputable brand will do for recreational diving.

For technical diving, for me, personally, all my experience is with Buhlmann ZHL-16B/C with Gradient Factors and that is what I will be sticking to for the foreseeable future. I would not dive a computer that used any other algorithm (me, personally) - unless it was just to use it in gauge mode and follow a written plan (that was created using Buhlmann w/GF).

I specifically reject technical diving using computers that incorporate biometric data into their calculations (presuming that option is turned on). The whole premise of technical diving is that you plan your dive. You get into the water knowing what your plan is and how much gas you expect to use. If your computer can increase your deco obligation based on, for example, your heart rate or skin temperature, then that means you could end up with a deco obligation that you don't have enough gas to meet - the antithesis of good technical diving.

It is my understanding that you can turn off the biometric aspects of the ScubaPro computers. With it off, the algorithm would be predictable and thus it might be okay for technical diving. But, again, just for me, personally, I have adopted and begun building my personal experience with the Buhlmann ZHL-16B/C w/GF algorithm. Nothing about the industry today suggests to me that I will find any kind of compelling reason to stray from the algorithm in the foreseeable future. I may change the GFs I use, but probably not the algorithm. And I don't think ScubaPro will make ANY kind of dent in the technical diving computer market until they provide an option to use Buhlmann w/GF.

I think accounting for environment/biometric factors is one reason that so many experienced tech divers tell all us newbs to take it slow. Because each diver needs to gradually acquire experience and pay attention to their body while doing so. So that each diver can develop a feeling for what works for them - without advancing their diving in big increments that could result in a big DCS hit, instead of just "feeling poorly" after a dive.

I tried to answer your #1, from my perspective, already. For your last question, my personal opinion is that the Teric represents the near-term future of dive computers. I think there will continue to be less expensive computers that are good quality and work just fine for people who only do sport diving. Their algorithms will stay proprietary. But, for anyone more serious, I am skeptical that anything will come out in the next 3 - 5 years that will make Teric owners really feel like they want or need to replace their Teric.
 
Tusa, Aqualung, Oceanic users –
  1. Does anyone use these computers for deco dives? If so how do you plan the dives? Estimating gradient factors for PZ+ I guess is a possibility and GFhi could be estimated based on the published NDLs but how would you approximate GFlo unless you actually took the computer on a deco dive?

Suunto, Mares users –
  1. How are the conservative factors established? How conservative are they? Are they related to or equivalent to the altitude settings?
  2. These computers allow altitude to be manually set. So does this not broaden the computer’s conservative factor range? For example say your computer had CF 0, 1, 2. And altitude setting (AS) 0, 1, 2, 3. Theoretically you have 12 conservative settings with the most conservative as CF2/AS3.

Keep in mind that neither of the above are designed for decompression diving. With the exception of Suunto EONs (does Mares have a "technical computer?) So I doubt you'll see anyone using them as primary computers on dives that incur more that a 10-15 minutes mandatory stop at around safety stop depth.

Suunto EON models are in the Ratio/Shearwater/OSTC bracket, and come with Suunto dive planner software.

AFAIK the best publicly available info on RGBM is a Wienke - O'Leary article from way back when, and that has a list of -- I'd say "considerations" -- that went into RGBM's conservatism. And I don;t think you'll find even that much for PZ+.

I never tried setting my computer to both altitude and extra safety. In fact I never upped my computer's "safety factor" from 0, so... the best I can offer is a couple that had their suunto gekkos' CF maxed out on -- I believe it was their first dive of the trip, same as ours -- and they had a non-mandatory 5-minute safety stop after an hour-long dive to 20-ish metres average depth. I.e. just your average reef dive.
 
A caveat with RGBM; because it is proprietary and takes into consideration and adjusts for multiday, repetitive diving, previous deeper dives and accent rates etc, a tech diver may be reluctant to use this algorithm because it may change the deco obligation during the dive itself which wasn’t planned for in terms of gas reserve.

This is not correct. They, at least Suunto RGBM, add an extra minute of optional safety stop. Ignore than and the NDL for the next dive may be reduced.

I am entirely happy doing Trimix deco dives with a Suunto, or a buddy with a Suunto.

The Scubapro Z+ thing sounds interesting and an advance on the pure disolved gas tracking.
 
Suunto, Mares users –
  1. How are the conservative factors established? How conservative are they? Are they related to or equivalent to the altitude settings?
  2. These computers allow altitude to be manually set. So does this not broaden the computer’s conservative factor range? For example say your computer had CF 0, 1, 2. And altitude setting (AS) 0, 1, 2, 3. Theoretically you have 12 conservative settings with the most conservative as CF2/AS3.

There is not a vast difference between p-2 (least conservative) and P0 (default) on my Helo2. These are the only two I use. Try some typical dives in DM5, maybe compare with GF plans.

I think the altitude should make a bigger difference but I never use that, usually being at sea level.

I, and lots of people I dive with, have done plenty of Suunto deco dives. Only one or two have been bent. One had a PFO and his buddy was fine, the other was a skin bend. This mean s I am reasonably confident that the Suuntos work in the circumstances I encounter. I set my Shearwater such that the dives are pretty similar. I will not use a GF hi of more than 85 unless I would otherwise run of of gas.
 
I, and lots of people I dive with, have done plenty of Suunto deco dives.

But you're talking EON, not Gekko, correct?
 
https://www.shearwater.com/products/teric/

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