Riding GF99 instead of mandatory/safety stops

[inquis]

I find it hard to believe that Shearwater named something GF99 that was unrelated to GF's.

The concept of GFs is to divide the space between Buhlmann's M-Value line and ambient into percentages. Then limit the ascent to a line between two percentages (GFLow & GFHigh) instead of the M-Value (100%). GF99 is your tissue loading relative to the full scale supersaturation. Yes, it's a little bit odd they named it GF99 rather than GF100, but they do the same thing with O2. 99% is the max you can specify. Perhaps a screen real estate thing.

 

[L13]

The concept of GFs is to divide the space between Buhlmann's M-Value line and ambient into percentages.

That was my understanding as well.

Then limit the ascent to a line between two percentages (GFLow & GFHigh) instead of the M-Value (100%). GF99 is your tissue loading relative to the full scale. Yes, it's a little bit odd they named it GF99 rather than GF100, but they do the same thing with O2. 99% is the max you can specify. Perhaps a screen real estate thing.

That is exactly what I thought GF99 was!

Thanks!

 

[inquis]

@EFX claims that the denominator for GF99 is (M-value - Inspired_Inert_preassue). Which doesn't make sense as compared to other GF's, but no one but me is stating different

Yes, I'm sure. See my posts above where I define GF99. You and LFMarm have (correctly) mentioned some inconsistencies that would occur if inspired inert pressure were in the denominator. GF99 doesn't abruptly change when you switch gases.

 

[BlueTrin]

The concept of GFs is to divide the space between Buhlmann's M-Value line and ambient into percentages. Then limit the ascent to a line between two percentages (GFLow & GFHigh) instead of the M-Value (100%). GF99 is your tissue loading relative to the full scale supersaturation. Yes, it's a little bit odd they named it GF99 rather than GF100, but they do the same thing with O2. 99% is the max you can specify. Perhaps a screen real estate thing.

The GF99 confused me too at first (it is technically GF100 from my understanding of the Shearwater manual)

 

[L13]

The GF99 confused me too at first (it is technically GF100 from my understanding)

I would think it would just be "GF" or "GFnow". I don't quite understand how the 100 (or 99) come in to play. It isn't part of the equation(I don't think).

 

[BlueTrin]

I would think it would just be "GF" or "GFnow". I don't quite understand how the 100 (or 99) come in to play. It isn't part of the equation(I don't think).

Yea GFNow or just GF or GFcu (for GF current) or GFPC (for GF percentage even though GF are already percentages) would be a better name, agree

 

[inquis]

GFnow would work. GF is a bit too vague. GF100 makes sense, because it is relative to 100% of Buhlmann's limit -- in contrast to the GF Line, the more conservative limit. And in Shearwater's world 99 = 100.

 

[dmaziuk]

GF99 doesn't abruptly change when you switch gases.

It changes on the leading TC switch, it just isn't that abrupt because M-values go down (and slope of M-value line gets shallower) as half-times go up.

 

[BlueTrin]

It changes on the leading TC switch, it just isn't that abrupt because M-values go down (and slope of M-value line gets shallower) as half-times go up.

You mean because it will extrapolate that the time to the last stop has changed?

 

[dmaziuk]

Because it's decreasing more or less monotonously. E.g. your fist stop is controlled by the fastest TC that also has the highest M-value, the next controlling compartment will have a lower one -- but not "abruptly" lower.

The computer has to extrapolate of course: you can't go up until all TCs have off-gassed enough, so when the leading TC changes (at a stop or during ascent), that has to be factored in before you tell the user how long and how deep their next stop is going to be.