Dive computers - how conservative?

[Rhone Man]

Whilst messing around one day, I found this interesting comparative table between models of various dive computers and various types of table.

(Here is the link to the original table).

As interesting as it was, it all looked pretty informal. Is anyone aware of any more formal published research in relation to comparing the various algorithms of the most popular dive computers on the market?

 

[Scott L]

Very informative. Thank you!

 

[RAWalker]

Mares I believe is RGBM like the Suunto I know for a fact at least the model MC2 is.
Also when doing a how conservative breakdown it would helpful to see the models that can be set to a conservative mode and what the difference on the chart would be.
This would be helpful for divers making a selection that would purchase a model and set it conservative until they are comfortable with their conditioning and the more liberal settings.
I know that Oceanic computers do have such a mode.

 

[maged_mmh]

Mares I believe is RGBM like the Suunto I know for a fact at least the model MC2 is.

I second that; also all Nemo models are.

 

[gcbryan]

Nice chart. I'd like to see a more detailed description of how each algorithm handles things like reverse profiles, two deco dives in a row, and all the other little things that some computers seem to penalize much more heavily than others.

Anecdotally we all know of some computers that are liberal on a first dive but where you incur extreme penalties for deco on a second dive but I've never seen it really discussed in detail.

 

[scubadada]

I have been interested in this topic for several years. I found chapter 24 in Deeper into Diving, Lippmann & Mitchell, JL Publications, 2005, very interesting. The dive computer analysis includes repetitive dives with reducing and increasing depths, multi-level dives with reducing and increasing depth, and cyclic bounce dives. Unfortunately, the list of computers tested is now outdated and incomplete but the analysis is, nevertheless, very interesting and informative. Relatively comtemporary computers from Suunto, Uwatec, Oceanic, and Cochran were included in the testing.

Enjoy, good diving, Craig

 

[Rhone Man]

It is interesting, in most discussions on dive computers, there seems to be an implicit assumption that "the more conservative, the better". I tend to disagree. If the computer spits out something that it knows is too conservative, then it gives me inaccurate data. As any actuary will tell you - it is pretty hard to risk manage with inaccurate data. I say: let me decide how conservative I want to be - just give me the best estimate of where the line is, and I will then work out how much safety margin I want.

I dive with a Suunto D9 and a Sherwood Profile, and I regularly have my Suunto telling me that I have a 4 minute decompression penalty whilst the Sherwood says that I still have 6 minutes of no-decompression time left on the dive. I know the guys at Suunto think they are being helpful, but really they are not.

 

[Kern]

How about, computers use a range of different algorithms. Each of the algorithms are based on different underlying assumptions about what's going on, such as gas uptake, off gassing, will or wont bubbles be formed , under what conditions etc. etc.

Some models say that if you exceed the 'M' value of the controlling compartment bubbles will form & give you DCS. Some think that bubbles will form but if they are kept bellow a critical volume you won't get DCS. Some will allow you to alter things by using gradient factors, others will allow you to make alterations by changing the radius of the bubbles allowed. And on it go's.

They're not spitting out info they know to be too conservative.They're giving you the correct info according to the model they use.

 

[Rhone Man]

They're not spitting out info they know to be too conservative.They're giving you the correct info according to the model they use.

This is true, but however sophisticated the algorithm, at the end of the day, they do just "spit out a number". If that number is consistently smaller than both other algorithms, and what practice has shown to be safe, then that number is less useful that one which is consistent with both those things.

 

[scubadada]

You can increase the conservatism of a liberal dive computer to meet your needs, however, you can do nothing to make a conservative computer more liberal.

I believe the single best source of information on this topic can be found in Deco for Divers, Powell, AquaPress, 2008. It is concise but thorough, up to date, very understandable, and has many illustrative figures and tables. Highly recommended reading for those interesting in a deeper (so to speak) understanding.

Good diving, Craig