ceiling/GF

[rsingler]

@Shearwater , here is my thought.
Sorry, sometimes pencil and paper is just...faster.

You could still continue the dotted GF line past the first stop, but with a narrow arrowed GF high scale, it becomes a touch more obvious that the diver is starting from ambient, and has his/her first stop at GF Lo.

My 2¢. Thank you for engaging with us!!!

Diving Doc

 

[mcpowell]

@doctormike,
Ok, great example. I keep thinking “but something has to force that sinking diver to begin his ascent”...

I guess if nothing else, his air capacity will motivate him eventually. If you or @rsingler make it to GA, I owe you a beer, or a scotch, whichever you prefer.

 

[rsingler]

Version 2

The reason I would not do this, however, is that as you can see, the red dotted line eventually intersects ambient at a GF Low of zero (albeit at a depth deeper than the chosen max depth for the dive).
I think the message you want to deliver is that the diver ascends from ambient to a first stop depth where the GF Low is the chosen overpressure value.

 

[mcpowell]

@rsingler your first chart with paper and pen was exactly what I was trying to descibe a page or so back. I, of course, never thought of paper and pen. I was too bogged down trying to think of a way to get my adobe illustrator back up and running.

 

[Couv]

You WANT this book. A little dated, and before the NEDU study started to make bubble vs. gradient a little clearer, but as a place to start? Unsurpassed!

Deco for Divers: A Diver's Guide to Decompression Theory and Physiology https://www.amazon.com/dp/1905492294/ref=cm_sw_r_cp_apa_rPSSBbRJ48AV3

Great book, but did you send chart corrections to the author? I think I have a first run copy and the illustrations could use your help. Hopefully the later editions have it sorted.

 

[lermontov]

It. On another note, my name is also Mark Powell, but there’s no confusing us. He’s a lot more knowledgeable, but it was weird to see people refer to my name the first few times I read it. I was thinking “what the heck?”

its a sign

 

[KenGordon]

Version 2
View attachment 482453
The reason I would not do this, however, is that as you can see, the red dotted line eventually intersects ambient at a GF Low of zero (albeit at a depth deeper than the chosen max depth for the dive).
I think the message you want to deliver is that the diver ascends from ambient to a first stop depth where the GF Low is the chosen overpressure value.

You could take a look at how you represent the left hand side.

One of the differences between the various disolved gas models is where the origin is. For ZHL the origin is at an absolute pressure of zero so surfacing pressure is somewhere to the right of the origin.

Another point is that a dive computer probably doesn’t pick the first stop depth this way. What you describe is the ‘proper’ method put forward by Erik and how a planner will work. The computers typically base the GF low depth on the deepest ceiling so far. Otherwise a slow ascent which allows the ceiling to move up before getting to any actual stop would result in unduely low GF limits later in the ascent. Also, what does it mean to be ‘at’ a stop?

 

[KenGordon]

Great book, but did you send chart corrections to the author? I think I have a first run copy and the illustrations could use your help. Hopefully the later editions have it sorted.

He is correcting the charts on this thread, not the book.

 

[KenGordon]

And another thing.....

There are really 16 ‘m lines’ with different slopes and different origins. Then there are ascent lines, non existent of those is allowed to cross its own m line. So the actual depth limit line isn’t straight.

These diagrams also under emphasise how steep the typical limiting (fast) compartments’ m line is. The fastest compartment has a slope of 2, so allowed supersaturation increases twice as fast as depth (ignoring the initial offset).

 

[mcpowell]

Why are the GF Settings scaled differently?