Gradient Factors

[Deep Thought]

Think of Gradient Factors as a means to adjust the M values, or maximum tissue tension that is allowed for ascent without bubbling.  When the inert gas in your tissues reaches the Maximum, a stop would be required.  The straight M value or 100% of what is tolerated for ascent is the basis for the deco model.

Gradient Factors are then split into GF-Low and GF-high, the low affects the “Deep Stops” and the high affects your shallow stops.  If you set the first number at 50 then you are telling the computer that you only want to ascend to within 50% of the tolerable tissue tension, and it would add a stop deeper that required for the straight M value.  Keep in mind that the concept of Deep Stops is a concept only, that sound prudent but has most of its foundation in empirical data and not scientific.  The NAUI Deep Stop conference I attended about 6 years ago, has now been challenged by some researchers that think technical divers are spending too much time or emphasis on stopping too deep – too long.  The second number is typically set higher as general consensus is that shallow end of deco is time tested and sufficient.  Your setting for the second number is 90 and not unreasonable.

The Shearwater computers that I use have 30 / 85 as factory settings, and I have found this to be reasonable for a short fat mean basta rd ;-)

One thing to keep in mind is that decompression is not a perfect science, and people vary in susceptibility.  Nothing wrong with a bit of conservatism in deco planning.  Also remember the adage:  “is the person you ask advice on dive tables going to push your wheelchair for the rest of your life”?
 
Keep doing research, ask questions and do not accept the status quo, things change.  Just imagine, we used to tell divers to follow the smallest bubble on ascent.

Do you have Mel Clarks book on CCR Trimix Simplified?  She is a good diver and writes well.

Ron