Adjustable, and not opinionated. I would not buy anything that locks me out, insists on stops at a precise depth and at a precise time it has calculated in its little brain and beeps, stops counting, crashes, or otherwise fails if the rigid schedule it insists on is not precisely followed down to an inch-second, like some brands of computers do, e.g., if you choose to make a stop at 25 feet instead of 20. The primary goal of the computer should be to patiently obey the will of its owner, to adapt to the situation in real-time, and to make best effort to emit the maximum of valid and helpful information under any circumstances. Petrel works great.
What factor is most important to *you* when you choose a dive computer?
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BDSC
Contributor
I dive the Sherwood Wisdom console and if it broke tomorrow, I'd replace it with the very same. Numbers are large and easy to read, does nitrox, and is air integrated. Only a two button operation. Easy to replace the battery. My wife and I have been diving them for several years now and never a single problem.
The most important factor for me in the past was wireless air integration. Now that I'm diving a rebreather, adaptability is the most important feature. Consequently, I dive two Shearwater Petrel 2s, unless I'm sidemounting, where it will be two Hollis DG03s with wireless transmitters. Since I've fallen in love with the Petrel 2, it will probably join me on those sidemount dives. OW reefs on OC find me using just a single Petrel 2. Why the Petrel 2? Super easy to read, pretty intuitive to use and I can alter gasses on the fly. I only wish it had wireless SPGs as well.
To somewhat future proof your computer purchase, I think the most important but greatly overlooked feature is its Algorithm. Here's why, and I'll keep it simple.
Decompression Science is fast changing given new findings and research. In the late 90s and 2000s, Bubble model algorithms such as VPM, RGBM and the inclusion of Deep Stops were thought to be the best approach in reducing DCS risks. Many popular computers such as Suunto and Mares, use proprietary RGBM and includes Deep Stop features. They still do.
Today, leading decompression scientists and institutions such as the US Navy Experimental Diving Unit (NEDU) are concluding the opposite. They have done manned tests and have compiled evidence supporting that Bubble Models and Deep Stops increase DCS risks.
Given these new findings, the growing trend in Technical Diving is to use computers with Buhlmann ZHL16c algorithm with user customizable Gradient Factors (GF) AND to set the GFs for shallow stops (vs deep stops). But even that is a moving target based on new data and learnings. Just 3 years back the thinking of scientists was a GF of 40/70 (this is a major shift away from much lower GFLo and Higher GFHi in the 2000s). In the 2015 DAN conference in SA, leading decompression scientists have publicly mentioned and suggested GF of 50/70. So, the level of conservatism is moving and will possibly continue to move as more data is gathered.
With the exception of a few computers, almost all other computers are using proprietary algorithms including those with PZ+. PZ+ is marketed as based on Buhlmann ZHL16c but the problem is, we don't know, and the manufacturers are not saying, what modifications in GF (or anything else) they've implemented in the deco algo. That's a major concern today and into the future if new data supports a different twist to decompression application and we cannot change our current computers to conform to that.
Many will say that this is only a concern for Tec Divers doing deep/deco dives and it has little or no impact on recreational divers. Perhaps. But take a look at this:
Using PADI Tables, a dive to 30 meters (100 feet) has an NDL of 20 minutes, with a 3 minute required safety stop.
If we apply the same 30 meter (100 feet) dive for 20 minutes using Buhlmann ZHL16c, with 50/70 GF, our profile will look like this.
Depth in metric:
Depth Stop Run Mix pO2 EAD
Des 30 - 1 21 - -
Lvl 30 18 20 21 0.84 30
Asc 9 - 22 21 - -
Stp 9 0:40 23 21 0.40 9
Stp 6 2:00 25 21 0.34 6
Stp 3 7:00 32 21 0.27 3
Sfc - - 32 21 - -
Dive # 1, ZHL-C+GF 50/70
Elevation = 0 m
CNS = 5%
OTU's = 14
Decozone start = 21 m
Gas 21 = 1672 ltr.
This means that a ZHL16c Algo with 50/70 GF requires a 10 minute deco for a typical, traditional, recreational NDL dive to 30m (100 ft) for 20 minutes. More conservative than PADI tables. As a Tec diver and Instructor, I would err towards the more conservative ZHL16c 50/70 GF profile. It's not just about getting bent or not. It's also about the often ignored decompression stress that comes with every dive (eg post dive lethargy, sleepiness, tired feeling, etc) and its long term effect.
While I like the platform, form factor and other features found in a Suunto (I own two), Oceanic, Mares, Sherwood, Aqualung, etc, the non-disclosure of these manufacturers on their proprietary algorithms makes me pause if I should invest or recommend investment in these computers.
Only a few computers in the market today are using Buhlmann ZHL16c with user changeable GFs. They are Shearwater (I use a Petrel 2), Nitek, Hollis, OTSC, and a few more. But these computers are more expensive. However, with these computers, we can change the GFs as new research and recommendations emerge. Can't do that on a Suunto or Oceanic, etc.
I believe Manufacturers are listening to new data and research on decompression science. I wouldn't be surprise if in the near future, Suunto or Oceanic will deliver recreational computers with ZHL16c algo and changeable GFs, or at the very least, provide clear disclosure on GFs used when selecting conservatism levels. This is what Shearwater did in their Rec Mode on their Petrel's and Perdix.
Just my 2 bar thoughts.
Decompression Science is fast changing given new findings and research. In the late 90s and 2000s, Bubble model algorithms such as VPM, RGBM and the inclusion of Deep Stops were thought to be the best approach in reducing DCS risks. Many popular computers such as Suunto and Mares, use proprietary RGBM and includes Deep Stop features. They still do.
Today, leading decompression scientists and institutions such as the US Navy Experimental Diving Unit (NEDU) are concluding the opposite. They have done manned tests and have compiled evidence supporting that Bubble Models and Deep Stops increase DCS risks.
Given these new findings, the growing trend in Technical Diving is to use computers with Buhlmann ZHL16c algorithm with user customizable Gradient Factors (GF) AND to set the GFs for shallow stops (vs deep stops). But even that is a moving target based on new data and learnings. Just 3 years back the thinking of scientists was a GF of 40/70 (this is a major shift away from much lower GFLo and Higher GFHi in the 2000s). In the 2015 DAN conference in SA, leading decompression scientists have publicly mentioned and suggested GF of 50/70. So, the level of conservatism is moving and will possibly continue to move as more data is gathered.
With the exception of a few computers, almost all other computers are using proprietary algorithms including those with PZ+. PZ+ is marketed as based on Buhlmann ZHL16c but the problem is, we don't know, and the manufacturers are not saying, what modifications in GF (or anything else) they've implemented in the deco algo. That's a major concern today and into the future if new data supports a different twist to decompression application and we cannot change our current computers to conform to that.
Many will say that this is only a concern for Tec Divers doing deep/deco dives and it has little or no impact on recreational divers. Perhaps. But take a look at this:
Using PADI Tables, a dive to 30 meters (100 feet) has an NDL of 20 minutes, with a 3 minute required safety stop.
If we apply the same 30 meter (100 feet) dive for 20 minutes using Buhlmann ZHL16c, with 50/70 GF, our profile will look like this.
Depth in metric:
Depth Stop Run Mix pO2 EAD
Des 30 - 1 21 - -
Lvl 30 18 20 21 0.84 30
Asc 9 - 22 21 - -
Stp 9 0:40 23 21 0.40 9
Stp 6 2:00 25 21 0.34 6
Stp 3 7:00 32 21 0.27 3
Sfc - - 32 21 - -
Dive # 1, ZHL-C+GF 50/70
Elevation = 0 m
CNS = 5%
OTU's = 14
Decozone start = 21 m
Gas 21 = 1672 ltr.
This means that a ZHL16c Algo with 50/70 GF requires a 10 minute deco for a typical, traditional, recreational NDL dive to 30m (100 ft) for 20 minutes. More conservative than PADI tables. As a Tec diver and Instructor, I would err towards the more conservative ZHL16c 50/70 GF profile. It's not just about getting bent or not. It's also about the often ignored decompression stress that comes with every dive (eg post dive lethargy, sleepiness, tired feeling, etc) and its long term effect.
While I like the platform, form factor and other features found in a Suunto (I own two), Oceanic, Mares, Sherwood, Aqualung, etc, the non-disclosure of these manufacturers on their proprietary algorithms makes me pause if I should invest or recommend investment in these computers.
Only a few computers in the market today are using Buhlmann ZHL16c with user changeable GFs. They are Shearwater (I use a Petrel 2), Nitek, Hollis, OTSC, and a few more. But these computers are more expensive. However, with these computers, we can change the GFs as new research and recommendations emerge. Can't do that on a Suunto or Oceanic, etc.
I believe Manufacturers are listening to new data and research on decompression science. I wouldn't be surprise if in the near future, Suunto or Oceanic will deliver recreational computers with ZHL16c algo and changeable GFs, or at the very least, provide clear disclosure on GFs used when selecting conservatism levels. This is what Shearwater did in their Rec Mode on their Petrel's and Perdix.
Just my 2 bar thoughts.
Last edited:
CuzzA
Wetwork for Hire
@Macan do you have evidence to suggest that following a square no stop PADI table dive will result in the symptoms you described? I'm not trying to be argumentative, just looking to further the conversation.
< Note the smiley face to insure I come in peace regarding an always fiery debate.
I believe your statements are slightly contradictory. Many argue against buying computers with other algorithms other than B16 w/GF because they are TOO conservative, like Suunto's modified RGBM. Furthermore, for "some" divers it's probably best that they can't tinker with the algorithm. Lord knows many humans naturally like to push limits.
Also, the NEDU study did not rule out benefits to slightly deeper stops. GF's in and of themselves are an attempt to mimic bubble models with deeper stops. However, it's my understanding that we learned from the NEDU study that we should try to find a balance between fast tissues off gassing and slow tissues on gassing in regards to our early stops. Thus the shift to higher gflow numbers.
Furthermore, I'm not familiar with the other algorithms you mentioned, but you stated we don't know what they're doing, yet insinuate they may be dangerous, but perhaps they are nothing more than a B16 w/ 50/70 GF.
< Note the smiley face to insure I come in peace regarding an always fiery debate.I believe your statements are slightly contradictory. Many argue against buying computers with other algorithms other than B16 w/GF because they are TOO conservative, like Suunto's modified RGBM. Furthermore, for "some" divers it's probably best that they can't tinker with the algorithm. Lord knows many humans naturally like to push limits.
Also, the NEDU study did not rule out benefits to slightly deeper stops. GF's in and of themselves are an attempt to mimic bubble models with deeper stops. However, it's my understanding that we learned from the NEDU study that we should try to find a balance between fast tissues off gassing and slow tissues on gassing in regards to our early stops. Thus the shift to higher gflow numbers.
Furthermore, I'm not familiar with the other algorithms you mentioned, but you stated we don't know what they're doing, yet insinuate they may be dangerous, but perhaps they are nothing more than a B16 w/ 50/70 GF.
I used to require this to be my dive computer:
1. Nitrox capable.
2. Had to be able to look like a watch (I wanted to use it as a watch at work as well as a dive computer. $400 computer that was a watch = dual purpose to me)
3. Had to have the same algorithm as my dive buddy. Nothing raises more questions than having you and your buddy being told different information by your respective computers. That cause some people to ignore their computer and follow the dive buddy's computer. Not a safe situation to be in if something goes wrong.
1. Nitrox capable.
2. Had to be able to look like a watch (I wanted to use it as a watch at work as well as a dive computer. $400 computer that was a watch = dual purpose to me)
3. Had to have the same algorithm as my dive buddy. Nothing raises more questions than having you and your buddy being told different information by your respective computers. That cause some people to ignore their computer and follow the dive buddy's computer. Not a safe situation to be in if something goes wrong.
OP
Zhukov
Registered
I understand where you're coming from, but I have read all the books by Wienke, read the published papers, etc. and I think you may be over-stating the importance of algorithms. Take a look at the PADI RDP as I have it from back in the early 90s. The limits, especially for repetitive diving, are much "looser" than many of the newer tables - yet no one implied that the RDP was unsafe.
Each model can't be isolated to just a particular algorithm unless you take all the customization dive manufacturers put in their software as a whole. Deep stops could be bad (again), but is it something that becomes apparent when you take the algorithm that's encapsulated in the dove computer as a whole?
I submit that a computer that's too customizable is MORE dangerous in the hands of an average diver than a computer whose algorithm may not conform to the latest and greatest thinking. People could simply try to force it to give them the max bottom time in such a way that jeopardizes their safety.
Even the "old" style computers that relied on simple ZHL-6 algorithms were never attacked for being dangerous - or at least I never heard of them being sued. Nowadays, we have much more safety with built-in safety stops, much slower ascent rates, etc. and I feel very safe if you give me any of today's dive computers (or those of yesterday) and I dive with a modicum of common sense.
Most important for me are the algorithms available(NOT proprietary) and display.
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