Why no accurate computers?

[boulderjohn]

Ratio runs Buhlmann ZH-L16B

Based on my understanding that it was based on the limitations of computer processing, I have been predicting that computers would make that switch as computer processors improved.

 

[Gareth J]

@ Gareth J- Really experienced divers don't know! Thank you very much for typing all that information out for me!. Really appreciate it! Why are manufacturing companies using the C algorithm instead of the B algorithm the tables are made from? Do divers really need conservatism on top of more conservatism? If the tables have been used for decades, why more conservatism? With the costs associated with diving, divers should want as much dive time as possible. I possibly found the best computer to get me closest to my dive table NDLs, I'm waiting for Shearwater to reply back about the Teric and Perdix. The rep stated she believed their computer would do 95/95. She's double checking. Someone told me the Teric will do 99/99. Not looking to violate tables, just match them, then allow the computer to modify if I do a multi stage dive. Then add the gained NDL to my next dive as the tables allow. Of course if the computer already did all this figuring for me that would be a nice computer.

Again, thanks to everyone!

The C had modification to the faster compartments (as far as I remember), and to compensate for the fact that the inherent conservatism in a square profile is not there in a real time calculation.

Please also remember, decompression tables where originally designed for military divers. Super fit young men, where a percentage loss was acceptable. Or for the commercial diving industry, where dive, bend and fix was a standard practice. With chambers, mounted on the boat you can afford this.

Killing or bending recreational divers is frowned upon. A 'percentage loss' of recreational divers is not a good sales or marketing policy. You will note, that diving accidents, or dci is heavily down played by the recreational diver training companies. [This risk aversion is also why decompression diving is frowned upon in the USA, until you go 'tech']
Also, there is a wide range of recreational divers, from the gym rats, to the larger gentlemen or ladies. So adding conservatism to the model stops the customers getting bent and taking the manufactures to court!

The Shearwater range are technical computers. So will be using a variant of Buhlmann with user changeable gradient factors.
If you are not using them in 'recreational mode', and intend to use GF's. I would strongly recommend you get some extra tuition so you know what they are doing and how they work.


It is also generally bad practice to mix table and computer diving. It is good practice to plan the dive before getting in the water. This includes the dive time, depth, and expected decompression obligations, also the required gas for the dive, and the gas for a just deeper, just longer. It also means if your computer is giving stupid information, you have a reality check.

Gareth

 

[Edward3c]

Thanks. Yes, that was described upthread, I decided not to footnote it for the table. So for a no stop dive to 90 feet on air, The BSAC bottom time would be 21 1/2 min, assuming an ascent rate of 30 ft/min and a SS at 15 feet.

@BurhanMuntasser posted the same for NAUI. I did not know that and could not quickly find that definition. Can somebody help me with a reference for that? Thanks

I think a little maths practise. 27m to 6m is 21m, ascent rate of 15m per min that's 1.4 minutes not the 2.5 you've stated.

 

[Barnaby'sDad]

Why not just get a Nitrox cert, set your computer to Nitrox (ex. 32%), and enjoy longer bottom times at 90’ that way?

 

[Edward3c]

Why not just get a Nitrox cert, set your computer to Nitrox (ex. 32%), and enjoy longer bottom times at 90’ that way?

Spoil sport, just as we were about to go down a rabbit hole.

 

[Gareth J]

Why not just get a Nitrox cert, set your computer to Nitrox (ex. 32%), and enjoy longer bottom times at 90’ that way?

We've all been explains how and why, and you've just fixed the issue by stating the obvious.

 

[scubadada]

I think a little maths practise. 27m to 6m is 21m, ascent rate of 15m per min that's 1.4 minutes not the 2.5 you've stated.

Thanks so much. I am imperially bound and we ascend at 30 ft/min, not 49.2 ft/min . Of course, if this is the ascent rate used for the BSAC tables, you are correct. Why did BSAC use time to stop rather than time left bottom, do you know? BSAC was not adapted for computer use, is that correct?

 

[Barnaby'sDad]

We've all been explains how and why, and you've just fixed the issue by stating the obvious.

Lol. Running 30%, even my RGBM computer is generous with bottom times at ~100’. I did three ~100’ dives one day and never came away thinking that I was getting cheated in the NDL department.

Nitrox...it’s almost as good as the Shearwater Kool-Aid.

 

[Gareth J]

Thanks so much. I am imperially bound and we ascend at 30 ft/min, not 49.2 ft/min . Of course, if this is the ascent rate used for the BSAC tables, you are correct

@scubadada, thank you, and I genuinely mean that.

You have just demonstrated a point made earlier in the thread. All tables have rules, they are not necessarily the same table to table. Applying a 'rule' from one table to another, may make the new table you are using invalid.

BSAC tables use max descent rate = 30m/min. Ascent rate 15m/min to the first stop or the ascent check depth.

If you ascend slower than specified, you need to leave the bottom earlier. OR, you are now on the NEXT line of the table. Which if you where on the edge of the no-stop dive (18m, 37min), you now have a decompression stop. Or if it was a decompression dive, you would have additional decompression stops to complete.

 

[Happy Spearo]

@scubadada- Sir, I am using a Atmos Mission One. I changed the conservatism to the lowest setting to see if I could get my computers dive planner to match the NDL of my SSI dive tables. My instructor taught me to use tables and they were safe. I was taught to plan my dive and dive my plan. However during my Deep Dive Cert class I noticed my computer in dive plan mode would say my NDL was less then my tables stated. So if I plan my dive and use the tables NDL then my computer would alert stating I now need a deco stop which I didn't actually need according to my tables. So I started looking for a computer that would keep me from losing so much dive time. Like I said, I lose 8 minutes on the 90ft dive. SSI says 25 minutes, computer states 17 (As shown in your graph). If I paid a lot of money to go somewhere and dive a certain cool wreck or wall, I surely don't want to lose 8 minutes on a dive. At 100 ft I lose 7 minutes. To me this is not acceptable performance of a dive computer. But then I found that most computers are to conservative. However, I was told the Teric might not be. Waiting on the final email from the rep. So, all of that made me wonder if the computers make a no deco stop (Rec dive) dive to short, they must also be making Tech dives shorter then need be (Could be wrong, don't have deco experience). I want to eventually do 330ft wall dives when I get enough experience under my belt.
I keep hearing the tables are to aggressive. They have been used for decades, don't understand that comment. Of course your still going to have some people get the bends because the tables are a approximation and some peoples bodies might not be able to handle them. I haven't had any issues using the tables. I read the tables were modified to meet the needs of MOST people. People need to judge for themselves. Also, People state no one square dives. Probably mostly true but the square dive profile is basically your worst case scenario dive (You absorb the most Nitrogen). If your multi level diving your absorbing less nitrogen so you are technically already being more conservative with your diving and the need for a computer to be conservative on top of that seems to be to limiting of my dive time. I didn't realize my question was so technical. I just wanted some conformity between my tables and my computer to remain safe. With the computers being programed differently so they don't correspond with the tables a new diver can't check them against each other which I see as unsafe and computers should be sold as corresponding to agency tables. (With the ability for the conservatism to be customized higher if the diver wants). I don't have my computer with me so I can't say what the conservative numbers are right now.