L13
Contributor
@lowwall is right about the definitions of GF Low and GF High in Baker's paper, and in the implementation by most dive computers and planners. But, @inquisit is right that the basic mathematical model proposed by Baker is perfectly able to handle a GF Deep higher than GF Surface definition of 2 GFs, though the High and Low names no longer make sense. The model can even handle GFs greater than 100.
GF Low << GF High was proposed By Baker based on the idea (from bubble model/deep stop hypothesis) that preventing bubbles in fast tissues early in deco was more important.
EDIT: This choice of GFs is no longer considered consistent with modern evidence, but the core model is still considered the best so far.
The modern evidence seems to indicate that GF Low ~= 0.83 GF High is probably a better choice.
If we hypothesized that preventing ongassing by slow tissues was more important than preventing bubbles in fast tissues, then GF Deep > GF Surface would make sense.
EDIT: I know of no evidence based reason to pick this choice.
Here is (my, worth half what you paid for it) summary of gradient factors based on modern research, in order from more confident to fairly uncertain but based on expert (not me) judgement.
GF Low << GF High was proposed By Baker based on the idea (from bubble model/deep stop hypothesis) that preventing bubbles in fast tissues early in deco was more important.
EDIT: This choice of GFs is no longer considered consistent with modern evidence, but the core model is still considered the best so far.
The modern evidence seems to indicate that GF Low ~= 0.83 GF High is probably a better choice.
If we hypothesized that preventing ongassing by slow tissues was more important than preventing bubbles in fast tissues, then GF Deep > GF Surface would make sense.
EDIT: I know of no evidence based reason to pick this choice.
Here is (my, worth half what you paid for it) summary of gradient factors based on modern research, in order from more confident to fairly uncertain but based on expert (not me) judgement.
- A lower GF High is more conservative than a higher GF High (but too low is impractical without a chamber)
- If GF High > 60%, GF Low > 50% is more conservative than GF Low < 50%.
- GF Low < or = GF High is probably more conservative than GF Deep > GF Surface
- GF Low ~= 0.83 GF High might be most conservative for a given GF High