Recreational Ascent Rate in the last 15 feet

[Jay]

A 2c feature request: Ability to graph GF99(Current) and SurfacingGF, and also to add CurrentGF to the Information Box that appears on the screen.

As I said, the heat map is already a plot of exactly that information. I created a pull request Add current GF to infobox by atdotde · Pull Request #2409 · Subsurface-divelog/subsurface that adds the numerical value to the infobox.

What kind of analysis are you expecting to do with this value?

Thanks for creating the request.

Re the Surfacing_GF graph aspect of the request - it's so that it can be seen over the entire course of the dive. On an imported dive that would inform you where you 'gained' that SurfGF decrease (especially for divers that don't have a DC with that info on it - and for divers that do, it's much better than semi-narked recall (and much easier than scrolling over the diver and creating the graphic in your head). For a planned dive, I think it would be educational to see how ascent rates at different aspects of the dive affect SurfGF ... i.e. a lot of the focus of this thread.

For GF_Current request (mainly the graphic aspect), my main reason for that request comes from a discussion in the Tec forum about how some divers target their GFCurrent.

 

[rsingler]

This is the answer to the discrepancy between my ss and Subsurface. Baker and I are calculating % of the m-value pressure (item 1 method above) where subsurface is calculating a percentage of GF which is item 2 above. The item 2 calculation will produce lower GF99 and SurfGF numbers than the calculation with item 1.

It took me a few minutes to figure out what EFX meant here. For the edification of those that think in pictures like I do, I think this is what @EFX meant about his Item 1 computations (in blue) coming out with a higher percentage than SubSurface Item 2 computations (in orange). The graphic is from page 7 of the Understanding M-values paper referenced above.

As he suggests, the same leading tissue compartment pressure will give two different numbers depending upon whether the denominator is absolute pressure or ambient pressure (sortof).

 

[rsingler]

I will provide a major revision of my ss that will give the user a choice between these options. So, to be clear, the %AoM on the ss does not equal GF99 or SurfGF as most users here have interpreted it.

I think any change that will have your output agree with other popular programs will increase its usefulness, for those of us that are interested in looking at the compartments in more detail. Thank you for considering this!

 

[EFX]

It took me a few minutes to figure out what EFX meant here. For the edification of those that think in pictures like I do, I think this is what @EFX meant about his Item 1 computations (in blue) coming out with a higher percentage than SubSurface Item 2 computations (in orange). The graphic is from page 7 of the Understanding M-values paper referenced above.

As he suggests, the same leading tissue compartment pressure will give two different numbers depending upon whether the denominator is absolute pressure or ambient pressure (sortof).
View attachment 552445

Yes, thank you for this clarification. This is exactly what I meant.

 

[FreeFlyFreak]

I think any change that will have your output agree with other popular programs will increase its usefulness, for those of us that are interested in looking at the compartments in more detail. Thank you for considering this!

More like essential for usefulness.

I don't want to compare against a compartment pressure of zero.

It only matters to compare your compartment pressures against ambient, at whatever depth you are at (GF99) or at the surface (GFsurf).
The surface (sea level) is 1 atm +/- smallish weather pressure changes.
Therefore the orange line pressure gradient is the only one that matters for diving. Or the third line not shown which would be the equivalent of SurfGF.

 

[rsingler]

I don't want to compare against a compartment pressure of zero.

It only matters to compare your compartment pressures against ambient, at whatever depth you are at (GF99) or at the surface (GFsurf).
The surface (sea level) is 1 atm +/- smallish weather pressure changes.

Well, to be fair to @EFX, Subsurface does exactly that with the heat map, I believe. If you read the fine print in the Help Section, this graph

is plotted against absolute pressure, not against ambient. @atdotde can comment, if I've mixed this up.
But ambient is the top of the green section in the little graphic in the floating box that accompanies the cursor. And "equilibrium pressure" (the lower black line) will lie in a position within the green section on the graph based upon the partial pressure of inert gas in ambient pressure (79% in Air at the surface, at equilibrium).
So it would appear that SubSurface shows both phenomena. This also explains why the heat map doesn't match up against GF99, I think.

 

[FreeFlyFreak]

Well, to be fair to @EFX, Subsurface does exactly that with the heat map, I believe. If you read the fine print in the Help Section, this graph
View attachment 552559
is plotted against absolute pressure, not against ambient. @atdotde can comment, if I've mixed this up.
But ambient is the top of the green section in the little graphic in the floating box that accompanies the cursor. And "equilibrium pressure" (the lower black line) will lie in a position within the green section on the graph based upon the partial pressure of inert gas in ambient pressure (79% in Air at the surface, at equilibrium).
So it would appear that SubSurface shows both phenomena. This also explains why the heat map doesn't match up against GF99, I think.

Well EFX was apparently following Bakers lead, which is more than understandable.
The real question is why does Baker use this method.
It seems odd to me, but I am certainly no expert in the field, just trying to learn something, and gain more than a rudimentary understanding.
I would love to find out.

 

[rsingler]

The method Baker used allows comparison of methodolgies, and is applicable across the spectrum. As seen below, SubSurface is able to compare a GF model with a VPM model using deep stops. The display of heat maps graphed against absolute atmospheres, rather than Gradient Factors, allows comparison with a model that does not use Gradient Factors. This is a screenshot from the Help file in SubSurface.

This pair of graphics displays in a nutshell, the difference between a decompression methodology that protects fast tissues from bubble expansion at the expense of greater gas absorption in slow compartments,
versus a methodology that allows greater stress on fast tissues in order to protect slower compartments from offgassing stress at the surface.
The two heat maps are markedly different, most particularly early in ascent, and near the surface.

 

[FreeFlyFreak]

The method Baker used allows comparison of methodolgies, and is applicable across the spectrum. As seen below, SubSurface is able to compare a GF model with a VPM model using deep stops.

Ah, that makes sense.

I need to dig into that Subsurface help file after I get home from Thanksgiving visit to Penngrove CA.

 

[atdotde]

The heatmap is also normalized with respect to ambient pressure: as you can see, a partial tissue pressure that equals ambient pressure is always black, if it is below the color is blueish above green and yellow. The way to see this is to look at ascents: the tissues are not so fast in following but the color changes thanks to changing ambient pressure.

As said much earlier, the absolute pressure is represented in the ceilings. Those don’t change quickly upon ascents.