Logging how far I pushed the nitrogen (now a Perdix AI; was a Oceanic DataTrans)

[tursiops]

Where is the extra work?
There are also dive operations that penalize you if your computers goes into deco, so why have it do that if it is unnecessary?

 

[scubadada]

Sure but you could just set it to what you want to get out of the water at like 75, and then if you need to get our sooner look at your surface gf and see how much risk you’re going to take on.

You’re doing a bunch of extra work to avoid having your computer tell you you’re in deco.

No extra work, my NDL and SurfGF are both on my home screen, to peruse at any time.

 

[tursiops]

No extra work, my NDL and SurfGF are both on my home screen, to peruse at any time.

ditto

 

[lairdb]

To be honest, I have never paid any attention to the nitrogen loading graph and have only paid attention to my NDL, of course the two are correlated.

Right -- during the dive, I just used the NDL (the DataTrans also helpfully made more prominent whichever was lower, NDL or GTR).

But after the dive, I found the "max" and "finish" graph measures interesting, as a sort of nitrogen intensity score.

Though not perfect, a GF high of 95 is similar to DSAT, is that what you run? [...] Specifically, I'm talking about SurfGF.

Yes, 45/95. Your mention of SurfGF is interesting -- I suppose what I'm thinking of is related. Thinking further, and re-reviewing the documents, I think what I'm thinking of might be the GF99, making the data points I'm imagining the the maximum and the ending GF99.

Or is it actually SurfGF? Re-re-reading, I think it's SurfGF. So, the data I'm used to recording from the DataTrans corresponds to MaxSurfGF and EndSurfGF.

Actually, my GF-high is the worst I want to get out of the water at. Preferably, I'll get out at a lower GF. That's what SurfGF allows me to do.

No extra work, my NDL and SurfGF are both on my home screen, to peruse at any time.

At any time during the dive. It seems useful, or at least interesting to me, to view MaxSurfGF and EndSurfGF after the dive, and I don't see those on the log screens.

(Edit to revise my thinking from GF99 to SurfGF.)

 

[scubadada]

Hi @lairdb

As you see from the graph in post #5, the GF99/or GF, does not go up until you start making your ascent from your no stop dive. It decreases at the safety stop and then goes up markedly during the final assent. At the surface, the GF99/GF = SurfGF and is available as the end surface GF in the dive stats.

Again, the SurfGF is the GF you would have if you surfaced instantaneously, no ascent time, no safety stop. I think that what you would like to see is your max SurfGF and your actually surfacing GF. Unfortunately, SurfGF is not tracked and cannot be viewed in the Shearwater Cloud. Quite a while ago I suggested that SurfGF be tracked and available on the graph. They acknowledged my request and said it would be evaluated, along with many other requests. For now, you would have to track your max SurfGF manually during the dive. I have never spent the time doing that.

 

[lairdb]

As you see from the graph in post #5, the GF99/or GF, does not go up until you start making your ascent from your no stop dive. It decreases at the safety stop and then goes up markedly during the final assent. At the surface, the GF99/GF = SurfGF and is available as the end surface GF in the dive stats.

Again, the SurfGF is the GF you would have if you surfaced instantaneously, no ascent time, no safety stop. I think that what you would like to see is your max SurfGF and your actually surfacing GF. Unfortunately, SurfGF is not tracked and cannot be viewed in the Shearwater Cloud. Quite a while ago I suggested that SurfGF be tracked and available on the graph. They acknowledged my request and said it would be evaluated, along with many other requests. For now, you would have to track your max SurfGF manually during the dive. I have never spent the time doing that.

Right -- it makes it harder to grasp GF and GF99 with so few examples in the manual, but looking closely at the charts in both ShearwaterCloud and in Subsurface make it clearer.

I didn't dig into the Shearwater database to see what's captured, but I did a uddf export to Subsurface, and from that Subsurface will calculate a SurfaceGF continuously in the graph data, based on it's own Buhlmann model.

Here's 10m40s in on an example dive of mine
UDDF datapoint:

          <waypoint>
            <cns>3</cns>
            <depth>31.280489</depth>
            <divetime>640</divetime>
            <tankpressure ref="T1">14603101</tankpressure>
            <tankpressure ref="T2">14616891</tankpressure>
            <temperature>298.15</temperature>
            <nodecotime>3</nodecotime>
          </waypoint>

Shearwater Cloud:

Subsurface:

...showing a SurfGF of 89%. (And a different "NDL" and "NDL (calc)" from what Shearwater shows. Hmmm.)


Here's the largest SurfGF I could find in the Subsurface chart for that same dive, captured during the ascent:

...and from Shearwater Cloud:

(I think what's happening here is that the controlling compartment is no longer the fastest -- the fast compartments are saturated, but the slow compartments are still on-gassing, so the SurfGF is rising, as those will be slower to offgas, even though the NDL has started to rise. In this way it's not quite parallel to the Oceanic barchart, but probably a better measure of nitrogen intensity score.)

If I did the import, I could then use Subsurface to look at my MaxSurfGF and my EndSurfGF. That gives me (for whatever little it's worth) a quantitative datapoint to compare this dive
95% MaxSurfGF; 67% EndSurfGF; 121fsw max; 67fsw avg; 30m30s
...to a later dive with
25% MaxSurfGF; 24% EndSurfGF; 26fsw max; 20fsw avg; 60m50s

It would be nice to have at least EndSurfGF (which Shearwater exposes in Shearwater Cloud, making me suspect it's logged) exposed in the onboard log display.

 

[Belzelbub]

Shearwater Cloud:
View attachment 745586
Subsurface:
View attachment 745585

...showing a SurfGF of 89%. (And a different "NDL" and "NDL (calc)" from what Shearwater shows. Hmmm.)

That could be due to a couple of factors. First make sure the GF set in the computer and in Subsurface are the same. If they match, then it’s likely just due to the sampling rate. The dive computer has access to data in real time, but only saves to the log at a set interval. Subsurface only has access to the points recorded to the log. You can change the sampling rate, if you want, but with one minute difference, I’d say it’s close enough.

Also, have a look at the little graph on the upper left of the Subsurface info box. This represents the loading of the individual tissue compartments. So, you could use this to get a graphical image of your presumed tissue loading at various points of the dive.