Algorithms

[ArcticDiver]

I recently bought a new dive computer. Because the dealer said the Nitek Duo and the Zeagle N2iTion were "...the same computer", as did other advertising I picked the cheaper, the Zeagle.

Then I found they use different algorithms. The DiveRite uses a "Buhlmann ZH-L16" where the Zeagle uses a "Modified Swiss model, 12 compartment Algorithm by Randy Boherer".

I've tried previously without success to get information from manufacturers on their algorithms. So, I am hopeful someone here can educate me.

Just what are the diferences in these algorithms? Are they essentially the same? Dive times and profiles differ significantly?

 

[Mr Carcharodon]

Well Buhlmann was Swiss so it seems a fair guess that they both use the same general approach. ZH-L16 is code for Zurich 16 levels. Zurich is where Dr. Buhlmann did some if not all of his work. So it sounds like the two computers use 12 compartment v. a 16 compartment model using the same basic theory. ZH-L16 (1990) uses half times of 4 to 635 minutes. I am not familiar with Randy Boherer model so any comparison would be highly speculative. That said many newer models have incorporated gradient factors to keep tissue pressure gradients down and tissue pressures closer to ambient pressure during ascent. This has the effect of slowing the deeper part of the ascent down. So if you have a chance to compare the two computers see if the Zeagle has you coming back the the surface more slowly than the Nitek. Of course for shallow dives there may not be much difference.

 

[texdiveguy]

Interesting question.

 

[ArcticDiver]

Well, now I know a little more than before. I did Google Randy Boherer. Nothing except in association with IANTD. But, I could find no pertinent useful information on their site.

One thing is certain: Claims that the DiveRite and Zeagle computers are "the same computer" are false. They may look alike but they are not the same.

In the dive profiles I've used the Buhlman algorithm gave longer bottom times and shorter mandatory deco times that the Boherer alogrithm. But, with this limited sample it is very unclear WHY that was, or whether the same would be in other profiles. Hence, the search to discover exactly what the difference is.

Maybe someone else has some more useful info?

 

[masterof0]

Being an engineer, I am always interested in the bits and bytes on how things work. Being a noob to SCUBA, I approached it with the same mentality as I do my job. As I started asking questions, I ran in to the same road blocks that you are running into. Each vendor uses a slightly different calculation to provide safe diving times and mitigating as much risk as possible. Comparing two vendor's algorithms is like comparing dive tables from different agencies. Getting the actual algorithm is not likely going to happen, but understanding the tables helped me determine which ones made since for me. Knowing this led me to ask simple questions when I shopped around for a dive computer....Do you want to dive more conservatively or more aggressively with more bottom time?

Is this what you are trying to determine or are you truly interested in the actual calculations?

Being new to SCUBA, I still won't be able to answer your question for you because I have only researched a few vendors, but I think asking the question in a different way may help you get the actual information you are looking for.

 

[Diver0001]

What I figure is that most computer manufacturers fiddle with the algorithms a bit to make the proprietory. I mean, if the algorithms were public domain then there would be dirt cheap clones of most manufacturers computers for sale on every street corner in Hong Kong.

I remember seeing graphs of a number of algorithms plotted on an overlay and they all came out within a fairly narrow bandwidth.... Barring bugs in the software I'd say that these days it matters more what you DO with the information than anything else.

R..

 

[nilsdiver]

Being an engineer, I am always interested in the bits and bytes on how things work. Being a noob to SCUBA, I approached it with the same mentality as I do my job. As I started asking questions, I ran in to the same road blocks that you are running into. Each vendor uses a slightly different calculation to provide safe diving times and mitigating as much risk as possible. Comparing two vendor's algorithms is like comparing dive tables from different agencies. Getting the actual algorithm is not likely going to happen, but understanding the tables helped me determine which ones made since for me. Knowing this led me to ask simple questions when I shopped around for a dive computer....Do you want to dive more conservatively or more aggressively with more bottom time?

Is this what you are trying to determine or are you truly interested in the actual calculations?

Being new to SCUBA, I still won't be able to answer your question for you because I have only researched a few vendors, but I think asking the question in a different way may help you get the actual information you are looking for.

This is why I dive a bottom timer and not a computer. I'm not gonna trust some black box that company X will not tell me what it does to keep me safe. With a bottom timer the deco algorithm is in the hands of you and your team.

 

[texdiveguy]

I dive both a Tusa brand wrist 'Duo' and a Dive Rite branded wrist 'Duo', and both at the same time while conducting extended range air/nitrox dives........have never noticed any differences in the two's calculations, course one unit is primary and the second a back-up so I am not comparing them constantly during the dive. For my trimix diving both are set in gauge mode for custom cut deco table use. Dive Rite does advertise their algorithm as a 'Modified' Buhlmann ZH-L16.

 

[ianr33]

For what its worth I used to have the Tusa clone of the Duo. Whatever the exact algorithm may be it is obviously very Buhlmanish i.e. it knows nothing of deep stops. If I were using any of these computers for deco dives of any consequence I would dive tables from V-planner or similar and use the computer for a back up only.

 

[texdiveguy]

For what its worth I used to have the Tusa clone of the Duo. Whatever the exact algorithm may be it is obviously very Buhlmanish i.e. it knows nothing of deep stops. If I were using any of these computers for deco dives of any consequence I would dive tables from V-planner or similar and use the computer for a back up only.

Dive Rite: "Using a Modified Buhlmann ZH-L16 algorithm, the NiTek Duo can calculate decompression stop times for required stops as deep as 90-feet." I am assuming the Tusa unit is darn close to this.