Question What computers have GF99?

[tursiops]

Do you know why they picked the name "GF99"?

My guess is they only had 4 characters to play with. The counterpart to SurfGF would be CurrentGF, so I wish they had chosen CurrGF.

 

[lowwall]

No, "GF99" is the label Shearwater attributes to the "current" loading, where 0 is saturated (loading at ambient pressure at whatever depth) and 100 is oversaturated to Buhlmann's maximum value (again, at whatever depth or ambient pressure). If you change depth, GF99 would change (increasing as you ascend).

All computers show current loading. Not sure why you would prefer it in percentages instead of the usual minutes.

IMO, SurfGF is a useful addition to dive computer user interfaces. The little compartments heat map is potentially useful and is certainly interesting. But GF99 is just a worse version of NDL in minutes.

 

[tursiops]

All computers show current loading. Not sure why you would prefer it in percentages instead of the usual minutes.

IMO, SurfGF is a useful addition to dive computer user interfaces. The little compartments heat map is potentially useful and is certainly interesting. But GF99 is just a worse version of NDL in minutes.

I kinda like to keep things in the same units, for ease of comparison. So GF99 is easier to compare with my GFLow/High setting and with SurfGF than minutes would be. I suppose you'd like everything in minutes? How do you set your GF Low/High in minutes, and what does SurfGF mean if expressed in minutes?

 

[L13]

All computers show current loading. Not sure why you would prefer it in percentages instead of the usual minutes.

IMO, SurfGF is a useful addition to dive computer user interfaces. The little compartments heat map is potentially useful and is certainly interesting. But GF99 is just a worse version of NDL in minutes.

I don't think you understand GF99. It has no relationship to NDL. You may not understand NDL either.
Neither GF99 or NDL is not an indication of current inert gas loading.

NDL is measure of time until loading becomes a problem if you go directly to the surface, and provides no measure of current decompression stress. 15 min remaining NDL at 60 feet is a very different loading than 15 min remaining NDL at 100 feet. For a fixed current loading, NDL would be longer the shallower you are. If you are doing a decompression dive, NDL becomes undefined and is useless as a measure of anything.

GF99 is a measure of decompression stress. With a given loading you would have a very different GF99 at 60 feet vs. 100ft. For a fixed loading it would be higher the shallower you are. GF99 indicates current decompression stress as a fraction of the limit, regardless of if your NDL is 99 or NDL is 0/undefined and you are 6 hours into your 8 hours of deco from your deep deco dive.

 

[lowwall]

It took me a few reads, but I understand your approach. If we are defining decompression stress as the percentage of the allowable M value for the most loaded tissue compartment, then GF99 is a direct measure of decompression stress. OTOH, NDL and SurfGF are measures of decompression stress at the surface assuming an immediate standard rate direct ascent.

Ok, we agree on that?

But I think we disagree on the value of knowing your current GF versus a surface GF. What does it give you other than a rough minimum and maximum ascent indicator if for some reason your choose to ignore standard ascent rates?

Yes you could use it as a way to run a less conservative ascent if you decided to ignore your own gradient factors. But in that scenario, it's simply duplicating what SurfGF gives you. And the rest of the time, it seems to me that you would be better served with one of the other options; NDL in a planned no deco dive, or ceiling or +5 once in deco.

This seems to be Shearwater's take on it as well:
Evolution of Dive Planning - Shearwater Research (starting at the section titled "Real Time Management of Risk").

 

[Nick_Radov]

I'm not sure how many others even have surf gf. But maybe it will come to the Garmin in an update as well.

The Garmin Descent Mk2 has a Surface Gradient Factor (SurfGF) data field. If you want to see it then you have to add it to one of the dive data screens, it's not displayed by default.

But I don't really see much point. It's not telling me anything useful.

 

[inquis]

I personally don't get much out of GF99 during a dive. But I have found it useful after a dive when considering driving over a mountain pass to get home.

 

[lowwall]

I personally don't get much out of GF99 during a dive. But I have found it useful after a dive when considering driving over a mountain pass to get home.

If you'd used that 100% at 3m instead of 6m, you'd have some left for the start of the drive.

 

[inquis]

Starting at 6m gives me a head start. Plus since I'm driving solo, the O2 originally reserved for my buddy is mine all mine.

 

[leadduck]

The OSTC shows "Saturation" which I think is the same as Shearwater's "GF99".