What's your SurfGF and how does it compare to your (Rec) GFHi?

[dmaziuk]

I analyzed all my Shearwater Cloud graphs after a recent dive trip and I realized that most of the time I am barely off gassing until i am above my 15ft safety stop then it shoots up from 15 ft to the surface.

There's several names for this, or, rather, names for several aspects of this phenomenon. Including "sample bias" and "McNamara fallacy".

 

[FreeFlyFreak]

In OC Rec mode you can select Big [screen view] (sounds like your current setup) or Standard, which also gives the middle/extra row where you can add up to 3 items. (no need to go into Tec mode). FWIW on mine in Big I have NDL and T1, then in Standard that shifts up a row (so it's consistent viewing if I change display), and I have SurfGF, SAC and GTR in the centre, so deco related stuff is on the left, and tank pressure stuff is on the RHS.



I had both GF99 and SurfGF displayed on that row but now replaced GF99 with SAC as GF99 is too finicky and SurfGF tells you a lot.

Super slow is super nice

You must have a Teric.
I have a Petrel.
The row options are not exactly the same.

There's several names for this, or, rather, names for several aspects of this phenomenon. Including "sample bias" and "McNamara fallacy".

Yes I understand.

I was trained as a scientist many careers ago.
But being that I only have a sample of 2 to work with (me and buddy), and I analyse literally everything, I can't help it, It is what it is, complete with bias, fallacy and fantasy.
Plus I only need a sample of one to find what works for me, if anything.

 

[dmaziuk]

What I meant was, you can't only be off-gassing above your safety stop unless your max depth was your safety stop. You're better off looking at heat maps as time series, that'll show the much more complete picture.

 

[FreeFlyFreak]

What I meant was, you can't only be off-gassing above your safety stop unless your max depth was your safety stop. You're better off looking at heat maps as time series, that'll show the much more complete picture.

Correct. But I only show 1% GF from starting off the bottom until 15-20ft.
At 15ft I am generally 1-5%
I surface at 30-55 GF so the majority of the Deco stress on the NDL dives I do is in the last 15 ft to the surface.

 

[rsingler]

Correct. But I only show 1% GF from starting off the bottom until 15-20ft.
At 15ft I am generally 1-5%
I surface at 30-55 GF so the majority of the Deco stress on the NDL dives I do is in the last 15 ft to the surface.

Before everybody jumps on @FreeFlyFreak for what seems like improbable GFs at the end of his dive, note his total dive count. If true, perhaps he's not as aggressive or deep as you are right now. Let's be thoughtful here...
I think he's to be applauded for knowing this much of the science this early in his dive career.

 

[dmaziuk]

I have no idea what it's really plotting, but that's a separate story.

What I do know is that the algorithm will let you on-gas all the way to M0 modified by GF Hi, that's your NDL. If you ascend directly to safety stop from there, your gas loading will be all that on-gassing less some epsilon due to little off-gassing during ascent and to being a bit below the surface. So by definition all your off-gassing will happen at or above your safety stop.

It should be different on a sawtooth or triangular profile, but if you're not diving those, you should not see that.

PS or to put it another way, if you needed to stop and off-gas below your safety stop, you'd be on a "decompression" dive.

 

[FreeFlyFreak]

In reply to rslinger (forgot to quote)

16 dives total, not including a DSD that is unlogged.
12 recorded in Shearwater cloud.
Of the dives in tbe cloud
Max depth 85ft
Average depth 57ft
Average dive time 47 mins.

In my mind I imagined GF99 to increase all the way up.
According to my logs so far my GF99 basically stays at 1% up to 15-20 ft depending on the dive. Then increases rapidly from there to the surface.

It was quite the eye opener for me to realize that, it was not how I imagined it. I thank Shearwater for giving us that valuable information, even if the tissue pressure's are all theoretical, its all we have to work with.

 

[dmaziuk]

:sigh: M-value is a linear equation M = M0 + D*dM. If GF99 is showing your loading relative to that, as The Fine Manual says, then d'uh. Sit on the bottom until your NDL counts down to 0, then see what that plot looks like.

 

[FreeFlyFreak]

Before everybody jumps on @FreeFlyFreak for what seems like improbable GFs at the end of his dive, note his total dive count. If true, perhaps he's not as aggressive or deep as you are right now. Let's be thoughtful here...
I think he's to be applauded for knowing this much of the science this early in his dive career.

:sigh: M-value is a linear equation M = M0 + D*dM. If GF99 is showing your loading relative to that, as The Fine Manual says, then d'uh. Sit on the bottom until your NDL counts down to 0, then see what that plot looks like.

I don't want to sit on the bottom until my NDL is zero (yet)
That's the whole point of being a Rec NDL limit diver.

 

[dmaziuk]

I don't want to sit on the bottom until my NDL is zero (yet)
That's the whole point of being a Rec NDL limit diver.

That last bit's debatable, but you do understand that GF99 is plotting one moving target relative to another moving target, yes? For one tissue compartment out of 16, subject to change without notice?