Gradient Factors - What is Everyone Using?

[EFX]

70/90. Mostly rec dives with occasional light deco of less than 5 minutes.

 

[seeker242]

Rec dives low conservatism on the perdix AKA 45/95. For deco dives 40/85.

 

[ScubaWithTurk]

I currently dive 50/85 for all the dives that I do which includes rec and tech. I used to dive 40/85 and made the move to 50. I always feel pretty good post-dive so I am happy with my current settings.

Now that I have been out of the water for so long (thanks COVID) I may dial back my GFHigh to 75 and ramp my way back up to 85 but that can only happen if I am able to actually go dive.

These are dives in would be considered warm water with temps ranging from 19c to 35c

 

[CWK]

99/99 for recreational, but only surface when surface gf hits 75 or less. This can involve a safety stop of up to 10 mins.

Have not done tec diving for a while but would probably lean towards 75/75. The thinking behind this is that I would want to avoid any semblance of deep stops. My understanding is that gradient factors was introduced to simulate deep stops in Buhlmann and the lower the gf low, the deeper the deep stop that gf is going to simulate. Since the NEDU study suggests that deep stops may lead to more incidence of the bends, I would tend towards pure Buhlmann, which I believe is what you get when gf low is set to the same value as gf high. In this view, a value for gf low below gf high does not represent greater conservatism, instead it represents deeper deep stops.

I’m sure there are others who have a different opinion and I’m happy to learn.

 

[tursiops]

I would tend towards pure Buhlmann, which I believe is what you get when gf low is set to the same value as gf high.

CWK, "pure Buhlmann" would be 100/100. I'm sure 99/99 is close!
X/X, where X <100, is not pure Buhlmann, but rather has essentially introduced smaller m-factors....more conservatism...but is not "reshaping the curve" the way (say) 30/70 would.

 

[CWK]

CWK, "pure Buhlmann" would be 100/100. I'm sure 99/99 is close!
X/X, where X <100, is not pure Buhlmann, but rather has essentially introduced smaller m-factors....more conservatism...but is not "reshaping the curve" the way (say) 30/70 would.

Mel,

Buhlmann m value would be 100/100

If you go over m value, a setting of 10/75 would generate deeper first stops than a setting of 75/75.

 

[tursiops]

Mel,

Buhlmann m value would be 100/100

If you go over m value, a setting of 10/75 would generate deeper first stops than a setting of 75/75.

The 100 means 100% of the m-value.
80 would mean 80% of the m-value, so like using reduced m-values.
Yes, 10/75 is deeper first stops than 75/75. But 75/75 means longer stops than 100/100.

 

[rabe]

40/80 for tec diving

 

[CWK]

The 100 means 100% of the m-value.
80 would mean 80% of the m-value, so like using reduced m-values.
Yes, 10/75 is deeper first stops than 75/75. But 75/75 means longer stops than 100/100.

Agreed.

To me 75/75 is still pure Buhlmann. The gf high is calculated as a % of Buhlmann's theoretical m value. All it does is set a conservatism value expressed as a % of m value and generate deco stops according to Buhlmann's algorithm where appropriate. Gf low set to the same value as gf high, I think, tells the computer not to adjust Buhlmnn deco stops to generate deep stops.

 

[huwporter]

To me 75/75 is still pure Buhlmann. The gf high is calculated as a % of Buhlmann's theoretical m value. All it does is set a conservatism value expressed as a % of m value and generate deco stops according to Buhlmann's algorithm where appropriate. Gf low set to the same value as gf high, I think, tells the computer not to adjust Buhlmnn deco stops to generate deep stops.

This is not correct. There are no gradient factors in pure Buhlmann. Gradient factors 100/100 only will give a profile identical to pure Buhlmann; as soon as you set GF-Lo to be less than 100, you will generate stops that are deeper than pure Buhlmann, and are therefore 'deep stops'.

Incidentally, Prof. Buhlmann himself didn't suggest using "pure Buhlmann", he suggested using 95% of the m-value (...for young, fit, expendible military divers), which would be equivalent to gradient factors 95/95.

Edit - also worth noting that precisely none of the actual 'anti-deep-stops' debate has been saying we should eliminate all deep stops and use pure Buhlmann instead. The debate has always been about whether we are(/were) doing too many, too deep unnecessary deep stops and not enough time shallow to compensate for them, and that the most efficient deco has probably a reduced level (though not reduced to to zero) of deep stops relative to shallow time.