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 –
Suunto, Mares users –
Scubapro users –
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?
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 –
- 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 –
- How are the conservative factors established? How conservative are they? Are they related to or equivalent to the altitude settings?
- 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 –
- What has your experience been with the heart rate monitor? Do you use it?
- Have you ever had large heart rate spikes during a dive? What was the consequence?
- 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?
- 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?
