Info The Rule of 120

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

jale

Contributor
Messages
940
Reaction score
684
Are you misunderstanidng on purpose? Average depth can be easily calculated, but using is for nitrogen uptake/offgassing is fiction. As I said.
Hi
It s not a fiction. You can even get UW tables doing that :)
 
OP
tursiops

tursiops

Marine Scientist and Master Instructor
ScubaBoard Supporter
Scuba Instructor
Messages
15,888
Reaction score
15,392
Location
U.S. East Coast
# of dives
2500 - 4999
I use a form of ballpark dive planning that is taught by one of the most well-regarded agencies on the planet.
Why use "ballpark" when your well-regarded computer doesn't need to?
As a cave diver following mandatorily non-square profiles (gotta be at whatever depth the cave dictates) that are symetrical (the cave going out is the same as the cave going in), so whatever your average depth is RIGHT NOW is going to be your average depth when you get to the surface.
I don't think you mean this. Let's suppose the cave gets deeper and deeper, and you are halfway into it. Your average depth at that point does not yet include the deep portion, so when you finally complete the dive the averaged depth will be greater than it was part way into the dive. perhaps you mean the average doth at your turn-around is the same as it will be at your exit?
Which is why I keep average depth on my primary screen of one of my computers (as, apparently, an option that enough people are interested in that it's an option on the computer). So I don't need to calculate it. I can just look down.

But the issue is not how easy it is to get your average depth. the issue is whether it is valid for calculating nitrogen uptake and offgassing. Unless a century+ of research is wrong, it is not.
I have personally watched this play out as accurate to within a minute or two of what my dive computer, one of the most popular on the market, has calculated for 16 individual tissue compartments using math I couldn't possibly even describe.
I have seen this happen on hundreds if not thousands of dives.
I'm inclined to think that it works just fine.
I'm inclined to think it is a coincidence., based on the caves you dive, combined with your apparent willingness to believe it is close enough.
 
OP
tursiops

tursiops

Marine Scientist and Master Instructor
ScubaBoard Supporter
Scuba Instructor
Messages
15,888
Reaction score
15,392
Location
U.S. East Coast
# of dives
2500 - 4999
Hi
It s not a fiction. You can even get UW tables doing that :)
Tables are from.... GUE? They invented the fiction, of course their tables will agree with it.
Don't they mean the average bottom depth (for a not-quite square profile), not the average dive depth? That is another tangent linear approximation.
 

jale

Contributor
Messages
940
Reaction score
684
Tables are from.... GUE? They invented the fiction, of course their tables will agree with it.
Don't they mean the average bottom depth (for a not-quite square profile), not the average dive depth? That is another tangent linear approximation.
No they are not from GUE. The world is wide and not everything thing gravitates around the US.
We already talk about that but...
 
OP
tursiops

tursiops

Marine Scientist and Master Instructor
ScubaBoard Supporter
Scuba Instructor
Messages
15,888
Reaction score
15,392
Location
U.S. East Coast
# of dives
2500 - 4999
No they are not from GUE. The world is wide and not everything thing gravitates around the US.
We already talk about that but...
So who produces those tables? Do they define "average depth"?
 

jale

Contributor
Messages
940
Reaction score
684
So who produces those tables? Do they define "average depth"?
Told you already:
 

oya

Rebreather Pilot
Scuba Instructor
Messages
422
Reaction score
728
Location
Akumal, MX
# of dives
5000 - ∞
Let's suppose the cave gets deeper and deeper, and you are halfway into it. Your average depth at that point does not yet include the deep portion, so when you finally complete the dive the averaged depth will be greater than it was part way into the dive. perhaps you mean the average doth at your turn-around is the same as it will be at your exit?

If I'm partway into the deep portion and my average depth, right now, is 50 feet... if I turned, right now, when I got back to the surface my average depth would be 50 feet.
When I get to the deep portion and dig on whatever there was I went there to see and find that my average depth, right now, is 80 feet... and I turn, right now, my average depth will be 80 feet.
....
But here's where it gets fun.
Let's say I'm down at, whatever, 120 feet, but my average depth says 50 feet. That deep my computer is freaking out saying I've only got 2 minutes of no-deco left. It's wrong. I've got plenty of time.
Because of the symmetrical profile of the dive, by the time I get to the exit any deco I may have incurred will be cleared.
Yeah, that deep the average depth will go up pretty quickly and that needs to be taken into account.
By the time the average depth reaches 80 feet... 130-80 = 50.
So I've got 50 minutes of dive time. So I need to turn at minute 25 if I'm not in the mood to do deco (because it's going to take the same amount of time to swim home as it took to get here.
My computer may already be 5 minutes into deco at minute 20... but I've still got 5 minutes before I need to turn around.
...
You can suppose all you like, man. But I have safely performed hundreds of dives this way, watching the ballpark agree with the computer every single time and never had so much as a skin tingle.
 
OP
tursiops

tursiops

Marine Scientist and Master Instructor
ScubaBoard Supporter
Scuba Instructor
Messages
15,888
Reaction score
15,392
Location
U.S. East Coast
# of dives
2500 - 4999
Told you already:
So you are falling back on those COMEX tables, which do not apparently mean what you think they mean.
Everything in deco is approximation, isn't?
The great fall-back response. It is all approximate so let's just make stuff up and use it...
This is in the same category as "my opinion is just as valid as your opinion."
We are not talking about opinions.
We are talking about depth averaging as the input to a calculation of nitrogen uptake, which is exponentially related to depth, not linearly related to depth. Sure you may not be very wrong with your answer, but if that is good enough for you, go for it.
If I'm partway into the deep portion and my average depth, right now, is 50 feet... if I turned, right now, when I got back to the surface my average depth would be 50 feet.
When I get to the deep portion and dig on whatever there was I went there to see and find that my average depth, right now, is 80 feet... and I turn, right now, my average depth will be 80 feet.
....
But here's where it gets fun.
Let's say I'm down at, whatever, 120 feet, but my average depth says 50 feet. That deep my computer is freaking out saying I've only got 2 minutes of no-deco left. It's wrong. I've got plenty of time.
Because of the symmetrical profile of the dive, by the time I get to the exit any deco I may have incurred will be cleared.
Yeah, that deep the average depth will go up pretty quickly and that needs to be taken into account.
By the time the average depth reaches 80 feet... 130-80 = 50.
So I've got 50 minutes of dive time. So I need to turn at minute 25 if I'm not in the mood to do deco (because it's going to take the same amount of time to swim home as it took to get here.
My computer may already be 5 minutes into deco at minute 20... but I've still got 5 minutes before I need to turn around.
...
You can suppose all you like, man. But I have safely performed hundreds of dives this way, watching the ballpark agree with the computer every single time and never had so much as a skin tingle.
You are arguing with a narrow example that coincidentally works in a narrow set of conditions.
 

oya

Rebreather Pilot
Scuba Instructor
Messages
422
Reaction score
728
Location
Akumal, MX
# of dives
5000 - ∞
You are arguing with a narrow example that coincidentally works in a narrow set of conditions.
Yes, it is an obscure, narrow, off-the-wall, nearly-unheard-of example... that I do nearly every day of my life.
 
https://www.shearwater.com/products/perdix-ai/

Top Bottom