Nitrox tables going too?

[vladimir]

And than I started thinking, what for do I need a new PDC? Even the algorithms of the latest modells are based on assumptions and theories only.

Only? What about the millions of dives conducted using tables (or their equivalent) with a bends incidence of less than 1%? Does that not count as empirical data?

 

[explorer08]

Only? What about the millions of dives conducted using tables (or their equivalent) with a bends incidence of less than 1%? Does that not count as empirical data?

Oh yes, of course. If I calculate every multilevel dive (and that is the vast majority of rec dives) as a square profile dive, I add a fairly good safety marge, so no wonder that the safety record is pretty good.
Just what I pitty that I have to do so much unnecessary deco time than.

 

[vladimir]

Oh yes, of course. If I calculate every multilevel dive (and that is the vast majority of rec dives) as a square profile dive, I add a fairly good safety marge, so no wonder that the safety record is pretty good.
Just what I pitty that I have to do so much unnecessary deco time than.

All the dives conducted with computers are also using the "algorithms and assumptions" that were tested by the US Navy, or the NOAA, using tables. They continue to validate those algorithms and assumptions with empirical data every day.

 

[explorer08]

Only? What about the millions of dives conducted using tables (or their equivalent) with a bends incidence of less than 1%? Does that not count as empirical data?

All the dives conducted with computers are also using the "algorithms and assumptions" that were tested by the US Navy, or the NOAA, using tables. They continue to validate those algorithms and assumptions with empirical data every day.

Vladimir, I guess I shouldn't answer to anything that early in the morning.
After being awake now for several hours and after thinking again about your comment, I am quite sure that I got you a bit wrong.

So second try.

Of course all the decompression theories and algorithms contain the empirical data of millions of dives as well. But that doesn't matter.
There is only some very basic knowledge existing about decompression. Most of this knowledge is dating back to J.S. Haldane. All the rest is based on empirical data. And around these data scientists constructed some scientific explantions - the existing decompression theories. Than, based on these theories they developed algorithms. And you are absolutely true, every PDC as well as every dive table is working with one of these algorithms. And because at the time most of them have been developed, usually tables have been the state of technology, most of these algorithms have been tested with tables and later on they have been converted into PDC's. And allthough some of these theories are even contradicting others, they all work. And that is the most important basic in every decompression theory - What works, works!

The most important difference between tables and PDC's is that PDC's represent your actual dives much more precise than tables and they are much more convenient to handle, because you don't need to calculate anything, you just have to read what is on the display.

 

[The Chairman]

The most important difference between tables and PDC's is that PDC's represent your actual dives much more precise than tables and they are much more convenient to handle, because you don't need to calculate anything, you just have to read what is on the display.

Unfortunately, precision does not produce greater accuracy. Neither tables or PDCs actually try to measure the actual amount of N₂ dissolved in your system. That would take doppler readings and would still be a SWAG. PDCs are inherently LESS SAFE than tables due to the ability (proclivity?) of a diver to ride the NDLs all the way up to the surface. Training is needed to inform the diver of this danger. This is why I teach 2 minute half stops and a full five minute safety stop to all my classes. This effectively adds to the eroded safety margin built in to the algorithms.

 

[Kingpatzer]

PDCs are inherently LESS SAFE than tables due to the ability (proclivity?) of a diver to ride the NDLs all the way up to the surface. Training is needed to inform the diver of this danger.

That is true only if computers are only as conservative as tables. However, most computers are more conservative than tables. If you do a true square profile on a computer you will find that many manufacturers give you less bottom time than the tables do. However, because most dives are not square, the depth fluctuations result in a diver having more dive time. The exact effect of this additional time is not as well tested as square profiles.

 

[The Chairman]

That is true only if computers are only as conservative as tables.

I disagree. That is my opinion for the reasons given.

 

[boulderjohn]

All the dives conducted with computers are also using the "algorithms and assumptions" that were tested by the US Navy, or the NOAA, using tables. They continue to validate those algorithms and assumptions with empirical data every day.

I don't personally know any computers that are based on algorithms and assumptions that were tested by the Navy or NOAA. I suppose there are some, but I don't know what they are. I believe Oceanic and Sherwood use the DSAT results (essentially PADI) for theirs. Suunto uses a proprietary algorithm based on Bruce Weinke's RGBM theory. Many use a Buhlmann model. Some use VPM. Several of the tech computers allow you to choose from several different theories and assumptions and download the one you like best.

I don't think any of the ones I just named coincide all that closely with the old Navy model.

 

[Kingpatzer]

I disagree. That is my opinion for the reasons given.

Are you aware of any empirical study that shows computers are inherently more risky than tables?

I don't disagree, btw, that diver training needs to be different than for tables, and that divers need to not be 'flying the computer.' Rather, it is my understanding that many computers, if not most, being more conservative than tables makes the comparison non-trivial. It comes down to opinion rather than data. If I'm wrong and there is data out there to support your position, I'd be more than happy to admit that I'm wrong about yet something else

 

[vladimir]

I don't personally know any computers that are based on algorithms and assumptions that were tested by the Navy or NOAA. I suppose there are some, but I don't know what they are. I believe Oceanic and Sherwood use the DSAT results (essentially PADI) for theirs. Suunto uses a proprietary algorithm based on Bruce Weinke's RGBM theory. Many use a Buhlmann model. Some use VPM. Several of the tech computers allow you to choose from several different theories and assumptions and download the one you like best.

I don't think any of the ones I just named coincide all that closely with the old Navy model.

My mistake. What I meant to say is that every model is a curve-fitting exercise relying on the accumulated empirical data--much of which has been accumulated using those algorithms and assumptions. It was in response to the assertion that computers are based only on algorithms and assumptions. There is a great deal of empirical data to check any algorithm against. There is also empirical evidence from medicine to validate half-times underpinning decompression theories.