Rising GF99 after surfacing???

[VikingDives]

A couple of thoughts. No real evidence here, I'm just kind of "thinking out loud."

1. Is this an artifact of sampling? In other words, is SurfGF calculated based on the last 5 or 10 (or some other number) samples that are taken? If so, that might account for the rise.

2. Where is the computer when you're "at the surface?" When I surface, my computer is rarely at the surface of the water, it may be several feet under until I exit.

3. I could envision that the code for SurfGF has some wiggle room in it to account for changes in depth that might be affecting the surface calculations.

4. I think there may be some small discrepancies between sampling and logging. I haven't really tested it, but on my last deco dive, I did a very nice 1 foot per minute ascent from 10 feet to 3 feet. I was playing with staying within that foot for the entire minute and watching my computer the whole time. I did not see any deviations, but when I looked at the log, there was a 1 foot drop at one point that I do not remember. Maybe that happened, but I didn't see it.

Just some food for thought...

 

[rsingler]

Here are five dives, two deco and three no-stop.
I dive GF50/70 for deco.
Here's what the graph shows from 10 sec before surfacing until 16 sec after (when graph is truncated) compared with what the computer logged as end-dive GF.
-10s = 10 sec before surfacing
S = moment of surfacing
X/Y = depth in ft/GF99

Of concern is that NONE of the logged GF's for the dive matched the peak GF after surfacing.
Of concern is that the graph is truncated despite my telling the computer to not End Dive until 360 sec after surfacing.
Of concern is the 11-16% rise in my GF99 that I might never see unless I specifically loaded the dives in Shearwater Cloud and looked at the graph.

What is missing is that for two weeks I forgot to watch GF99 for six minutes after any dive.

What is reassuring is that peak GF never exceeded 70 after a deco dive (at least as graphed - I forgot to watch).

 

[scubadada]

Now up to version 2.10.2 and the problem persists.
My graph is still truncated (now 60 sec after reaching surface) despite specifying Dive End at 360 sec.
My graphs still show an increasing GF99 over that one minute, and the listed surfacing GF in the dive statistics is often as much as 11% lower than the max GF99 graphed before Cloud truncated my graph.
On my last Deco dive, after dawdling at 10' an extra few minutes (I dive 50/70), the GF99 max on the graph was 62%, while the data summary says my dive's surfacing GF was only 51% (which was true the instant I hit the surface).
I have not heard anything further from @Shearwater after my inquiry. Count me disappointed in them. 62% vs 51% is not insignificant, even if we don't really know what it means.

Hi Rob,

Did you refresh your inquiry with Shearwater with your new data with 2.10.2?

I am also using 2.10.2 and went back and looked at my last 8 dives. I have always used an end dive time of 10 min. These 8 dives only showed data for 20-50 seconds after surfacing. On older versions of the Cloud, I would see data for a much longer period of time after surfacing. I did see an increasing GF after surfacing on some occasions but, unfortunately, did not look at it systematically or record the information.

Nothing very dramatic in these most recent dives. End surfacing GF was usually recorded at a depth of 0 ft but sometimes and a depth of 1-2 ft. The end surfacing GF was the highest GF recorded on 6 of the dives, it went up 2% soon after surfacing on just 2 dives. During the short period recorded after surfacing, the GF always decreased, usually 1%. The GF went down 3% on one dive, 4% on one dive, and it went down 7% on one dive over just 30 seconds.

At least recently, my end surface GF would seem to be reasonably accurate, but I am unable to follow it very long after surfacing. I have asked Shearwater to add SurfGF to the Cloud graph as an additional piece of information. They've told me it's on the list for consideration for several years now.

 

[rsingler]

The end surfacing GF was the highest GF recorded on 6 of the dives, it went up 2% soon after surfacing on just 2 dives.

This is an interesting disparity compared with my most recent data.
I'm guessing it's just a data logging/computation lag. But the discrepancy is HUGE.
Here's minus 2 seconds before surfacing:

Here's Surfacing:

Here's Plus 14 sec after surfacing:

The blue line is when I hit zero feet.
Look at the GF99 before it's truncated. That's a 13% discrepancy!

The peak GF99 in this little pic above is close to my recalled SurGF just before surfacing.
See the first pics upthread from before I updated my Cloud software. There you begin to see the decline that we expect.

Yes, I need to bug Shearwater again. They were very prompt in replying to my query, suggesting that it was being looked at. Then, crickets.
EDIT: Just followed up on the ticket I opened with them...

 

[rsingler]

YET ANOTHER SHOUT-OUT TO SHEARWATER!

Even though it took two tries, I heard back from the software engineers.
What a comprehensive email!
It's just easier to paste in his reply:

Software Developer (Shearwater Research) Dec 1, 2023, 13:50 PST Hi Rob Thank you for reaching out. I'm from one of the software engineers and can help answer your questions. - Previously, dives have been clamped on the graph from surface to surface to help users visualize only the dive. The graph has been overhauled recently and there is now an option to remove this clamp to help users analyze any post-dive data they may require. For an example, please see the attached images and how the graph (in the background) becomes extended to include the entire dive duration when the clamped is removed. This should help resolve a few issues. - The ascent going from 3.3 ft to 0 ft is how the dive computer assess the diver surfacing and any depth under 3ft will be recorded as 0ft. The discrepancy you are viewing between the first 0 depth and the peak surface GF is a result of your dive computer still being in the water and calculating GF99 from the recorded the water pressure. So technically your head may be at 1atm, but your computer is more likely still at 1.1 atm (or something to that effect). - The discrepancy between the surface GF you see on the graph vs in the computer panel is due to my first point of how some displays have been clamped to when the diver first surfaces. The GF99 calculation for end surface GF has been updated in this most recent release and will now reflect the greatest GF99 value observed at the end of your dive. I hope this helps clear a few things up. All the best -- Eric Herbst Software Developer

I have replied to this message asking about implementation dates, as yet another new version (v2.10.2) does not appear to include the settings referred to above. However, I may have just missed the button that unclamps my data.

In any case, Shearwater has answered ALL of our questions:
1) the jump to 0.0 feet from 3.1 is a convention to end the dive, but offgassing calculations continue in the background
2) the logged GF for the dive will now be updated to the greatest GF99 observed at the end (I'm not sure how this will implement for divers that continue to clamp their graph, as there's an increase that they may not see shortly after surfacing)
3) we'll now have the option to display data from surfacing to stipulated "Dive End". Hooray!

See the attached graphic of an UNclamped dive that they sent with the e-mail.
Apart from @LandonL at Deep6, what other company can you think of that would be this responsive???
Thank you, @Shearwater !

Now, if only Santa Claus would bring me a new Petrel 3 for my JJ...

 

[attue]

thanks for your informations - that's great. Maybe it's the upcoming update as i also don't have the button clamp length. In my Windows-cloud-app I've only got the graph-grid-option.

 

[rsingler]

Just heard back from Shearwater.
The update with the new unclamping option will be here in early 2024.

 

[attue]

I am looking forward to the new update.... at my last dive I've got some odd numbers in the end-dive-surface logged again, as you can see in the dive-loggs below (we had to call the dive due to technical equipment problems). In subsurface I had surface GF at around 56, and shearwater showed me an end dive surface-gf of 255!!

EDIT: sorry, dont know why the picture-quality is so bad, as pictures are perfectly fine when opened at my desktop before uploading to the post.

 

[attue]

shearwater-cloud update (app and desktop) is out now - surface-end-gf is now approx. the same as the last shown surface-gf-value in subsurface (i've looked at 4 of my last 18 dives - it differs 0-4% - which for me isn't a problem. most of the dives only differ by 1 or 2%). That's fine for me - no more need to export them to subsurface. Have a nice weekend!

EDIT: sorry guys was too fast - had a closer look and both GF at subsurface and GF99 at sw-cloud match pretty much now- but thats at the point of the last logging point, where GF and surf-gf still can differ quite a lot (e.g. at one of my last dives GF=46% and surfGF=64)
Still think it would be better to log the last surfGF-value as the surface-end-gf-value.

cheers attue

 

[scubadada]

I updated to SW Cloud 2.11.0 today, some nice improvements including the unclamping option. I still wish they would add SurfGF to the graph.