What's your SurfGF and how does it compare to your (Rec) GFHi?

[Wibble]

Haven't read the whole thread yet but this is wrong. According to the teric manual, it is assumed you surfaced INSTANTLY not after a standard ascent rate. (Apologies if this was corrected later on).

SurfGF is a really nice indicator of how much of a decompression obligation you currently have. A simple number, the higher the SurfGF the greater the decompression time you have ahead. If an NDL dive the SurfGF will always be below 95 (or whatever your GF-hi is set to).

It's a nice indicator as it's a simple number that most people can understand without an in-depth knowledge of decompression theory or resorting to "Tissue compartment inert gas pressure"/depth diagrams.

 

[dmaziuk]

It seems to me that 95/95 is really pushing the limit just not to have a deco. Is that safe to try so hard not to have a deco when you are a rec diver ?

"Trying hard to avoid deco" may be an issue in some cases, but DSAT has worked very well for no-stop diving since PADI first published its RDP; "it ain't broken". 95/95 is not exactly DSAT but it's close enough at least for the first day or two so why not.

If you want to add extra conservatism because you're old, cold, hungover, and risk-averse, you're welcome to it -- with gradient factors or conservative levels, whatever your computer supports. And conversely if you're using a "conservative" computer and not running out of bottom time on your dives, what do you care about a setting that gives you "more NDL".

 

[scrane]

Haven't read the whole thread yet but this is wrong. According to the teric manual, it is assumed you surfaced INSTANTLY not after a standard ascent rate. (Apologies if this was corrected later on).

Yes. This has always confused me. What does "instantly" mean in practical terms?

 

[inquis]

What does "instantly" mean in practical terms?

It means the computation neglects any off-gassing and is therefore an upper bound on what you would actually have. It's easier to compute while remaining quite useful.

 

[Wibble]

Yes. This has always confused me. What does "instantly" mean in practical terms?

Imagine you're swimming along on the bottom looking at the SurfGF. That is what your current Gradient Factor would be if you were "magically and instantly" on the surface.


An example: a deeper dive last weekend at 60m/200ft for 40 minutes. As I was about to leave the bottom for the 80 minute decompression (as shown by the TTS - time to surface), the SurfGF read 408%. As the decompression progressed, this slowly reduced to 80%, at which point I ascended from the last stop to the surface without being bent.


Aside from an indication of how much decompression is required, SurfGF's also a great indicator of just how bent you would be if you "had" to get to the surface "now". 400% would be serious injury or death. 120% could mean you might get away with a minor bend (there's no guarantee!).

 

[stepfen]

Following this incredibly useful thread I would like to invite @dirkhh et al. to consider including in Subsurface's dive statistics the GF at the end of the dive ("end GF" or whatever it is called).
As this number is a good indication of how "aggressive" the dive was, having it is of very high importance I think (for us people who don't dive Shearwaters). I know the user can "manually" find it in the information box at the very end of the dive profile in Subsurface, but having it also as a number in the Information tab would be nicer I think.
Also, once we have this number for every dive, it will be possible to include it as info in the dive list and I think it will be really useful to do statistic based on it. For example it will be very interesting to be able to short dives to see which were more or less "risky", calculate average "end GF" over several dives, study progress of one's "end GF" over the years etc etc.
Maybe if several divers here show interest and we ask nicely @dirkhh , he might consider adding this to Subsurface. Hope for the best...
Thanks

 

[Divin'Papaw]

Following this incredibly useful thread I would like to invite @dirkhh et al. to consider including in Subsurface's dive statistics the GF at the end of the dive ("end GF" or whatever it is called).
As this number is a good indication of how "aggressive" the dive was, having it is of very high importance I think (for us people who don't dive Shearwaters). I know the user can "manually" find it in the information box at the very end of the dive profile in Subsurface, but having it also as a number in the Information tab would be nicer I think.
Also, once we have this number for every dive, it will be possible to include it as info in the dive list and I think it will be really useful to do statistic based on it. For example it will be very interesting to be able to short dives to see which were more or less "risky", calculate average "end GF" over several dives, study progress of one's "end GF" over the years etc etc.
Maybe if several divers here show interest and we ask nicely @dirkhh , he might consider adding this to Subsurface. Hope for the best...
Thanks

I've added End Surf GF to my custom dive log spreadsheet and I now track it for every dive. As you mention, it is a good data point to help measure how "aggressive" one dive was vs. another.

 

[dmaziuk]

Following this incredibly useful thread I would like to invite @dirkhh et al. to consider including in Subsurface's dive statistics the GF at the end of the dive ("end GF" or whatever it is called).
As this number is a good indication of how "aggressive" the dive was, having it is of very high importance I think (for us people who don't dive Shearwaters).

Personally I think if you want to see that: just turn on the heat map. Unlike Surfer GirlFriend it shows you all compartments, and throughout the entire dive too.

That said, it's a simple enough calculation that can be added to that little sliding popup box, so... create a feature request "issue" on github if there isn't one already.

 

[stepfen]

Personally I think if you want to see that: just turn on the heat map. Unlike Surfer GirlFriend it shows you all compartments, and throughout the entire dive too.

That said, it's a simple enough calculation that can be added to that little sliding popup box, so... create a feature request "issue" on github if there isn't one already.

I think what you mean is already there, here how the end of my latest dive looks like:

Now since we have this already, what I am talking about is to add this number to the other dive info (like SAC, Water temperature, duration etc), so that the user can further use it for dive analysis (compare it among dives, do statistics, short dives based on this, see how it evolved over the years etc).
Since the number and the means to do all these analyses are already there, it is a pity not to be able to do that especially given that this particular metric seems to be so important.

 

[dmaziuk]

I think what you mean is already there, here how the end of my latest dive looks like

Ah, I should update mine, or maybe check the menus and see what's been added since I last looked.