Diving with gradient factors for a new recreational diver

[tursiops]

"All sources agree" that it monotonically decreases with GF and thus as we decrease GF high below 75 the risk decreases to below "around" zero. Once pushed into negative numbers, it may in fact even protect the diver from future DCS on tomorrow's dive!

What nonsense you post. You extrapolate out-of-bounds what someone says, purposefully misinterpret it, and then make fun of it. It is not good humor, and it is terrible sarcasm.

 

[inquis]

I was mainly interested in the shape of the curve.

Looks monotonic to me.

 

[dmaziuk]

You guys are not fun. Who cares about risk reduction at P→0? Now negative values of risk, that's interesting and worth looking into.

 

[L13]

"All sources agree" that it monotonically decreases with GF and thus as we decrease GF high below 75 the risk decreases to below "around" zero. Once pushed into negative numbers, it may in fact even protect the diver from future DCS on tomorrow's dive!

I don't think you understand the mathematical concept of monotonic.

 

[EFX]

Is it monotonic or monotonous?!

 

[VikingDives]

Is it monotonic or monotonous?!

At this point, it is perhaps both

I appreciate more academic discussions. Though I just sit in the corner, nibbling a box of crayons most of the time.

 

[dmaziuk]

I don't think you understand the mathematical concept of monotonic.

I don't think you're familiar with overfitting and related data fallacies, like simpson's paradox, or surviorship bias.

Do you think SAUL's prediction that Craig posted upthread exactly mirrors the plot from Howie for the .2 isopleth because both sources independently arrived at the exact same curve from independent sets of empirical data?

 

[L13]

I don't think you're familiar with overfitting and related data fallacies, like simpson's paradox, or surviorship bias.

Actually, I am thoroughly familiar with them. This kind of mathematical analysis and it'ts pitfalls are what I do in my "day job." Simpsons' paradox is one of my favorites.

Do you think SAUL's prediction that Craig posted upthread exactly mirrors the plot from Howie for the .2 isopleth because both sources independently arrived at the exact same curve from independent sets of empirical data?

No, they have similar results because they are base on the same theories of bubble formation in supersaturated fluids, as are every model since Haldane. And, on extensive re-analysis of the same dive data since the collection of novel data is expensive and really only the domain of a major Navy, particularly the US Navy.

Can you point to any theory that fits the data better? can you point to meaningful data that they didn't take into account or that contradicts them?

The data is insufficient to derive precise answers. But it is more than adequate to validate the the principles underlying all current algorithms as (so far) better than all others (so far) proposed. It is more than adequate to determine the monotonic relationship between PDCS and Supersaturation. It is more than adequate to determine that the curve is non-linear and steeper at the GF=100 end than the GF=0 end. It is probably good enough to be fairly sure that the first derivative is also positive and monotonically increasing as well, though I would have to look closer to be sure.

Just because a conclusion from the data is not exactly correct doesn't mean it isn't usefully correct. For an example most people will understand: the fact that Newtonian physics and theory of gravity is wrong at relativistic speeds, does not make it meaningless or less useful in normal conditions. Which is why engineers everywhere rarely use Einsteins physics instead (unless they do orbital mechanics or other relatively esoteric work).

Any hypothesis that doesn't fit the data we do have (eg. 4% reduction in risk going from GF100 to GF50) is more wrong than the ones that do. Maybe as we get more date the hypothesis we have now will be superseded, or even invalidated. But until that data is in hand, you can't just pretend that they are meaningless. And most likely the new hypothesis will be refinements rather than wholesale rejections of what we have now.

 

[exodusmaximus]

Will it penalise you if you miss its "mandatory" "safety stop"**? Many lock you out of using it for 48h of dryness.

**A safety stop isn't mandatory. If it is, it's called decompression.

Stopping half way up is old school as most people consider stopping deep to on-gas seems an odd thing to do.

"Mandatory" safety stop will lick you out for 6 hours

 

[Wibble]

"Mandatory" safety stop will lick lock you out for 6 hours

Just to clarify, it's "mandatory" by the dive computer's programmers, but not mandatory for the diver who may well have more information or pressing circumstances. These could be using it as a backup computer and the primary computer's cleared the stops, maybe because the primary computer has a different algorithm or configuration (GFs), maybe you're close to clearing your stop and need to surface (this shouldn't get you bent and certainly not seriously). Maybe it was borrowed off of someone else. There's a whole host of reasons.

Therefore any dive computer that has mandatory lockout periods is not fit for purpose in serious diving.