Which article? ...
Which article? ...
Caution should be taken in setting your lowest gradient too low as you will still be absorbing nitrogen. This will cause the computer to extend stops in the 6 mtr region. Also setting the hi gradient higher than 90% has resulted in more cases of DCI. GUE recommend 30/90 although some prefer 20/80. JPlan allows you to play with these settings and view comparisons.[b said:Quote[/b] ]
Decoplanner Gradient Factors
Since Decoplanner gradient factors are mystifying to a lot of people, I figured we would be doing everyone a service by chatting about them for the benefit of those using Decoplanner.
I'll start, and get hammered by my lack of understanding, but I figure if I had questions about them someone else might be sitting there with the same problem and not want to say anything for fear of looking stupid. We DEFINITELY want to discourage this type of behavior on this board and encourage people to speak up...nobody will make you feel like an idiot just for asking stuff (please keep this in mind when I fuck this decoplanner stuff up ).
Anyway...gradient factors are used to adjust the dive profile giving the diver control over the conservatism and shape of his/her deco. Essential background reading is included in Decoplanner help files and also can be found here:
Although we won't talk about everything here, basically touching on gradient factors (GF) and the associated pressure graph will go a long way in furthering our mutual understanding over something this cryptic. IMHO, you have to read Baker's papers 5 times each before they start to make sense, so hopefully this will save someone a couple readings..
What They Do
GF Lo% controls the depth of the first stop (deep stops)
GF Hi% controls how close the tissue compartments are allowed to reach the M value line. A 0% gradient is equal to the ambient pressure line (neither off-gassing or on-gassing). A 100% gradient is equal to the M-value line and is the furthest point into the decompression zone settable in Decoplanner.
What The Hell Does That Mean
Set GF Lo% lower to drive your initial stops deeper.
Set GF Hi% lower to increase conservatism and lengthen deco or higher to decrease conservatism and shorten deco.
What The Hell is the Graph With No Legend?
The graph with no legend is the tissue pressure graph. After reading Eric Baker's article, "Understanding M-Values", you can make sense of this graph and use it to understand what is happening as you adjust gradient factors.
From Erik's paper, you will note that the zone in between the ambient pressure line (below) and the m-value line for a specific compartment (the colors match up on the graph for each compartment - see below) is the "decompression zone". By ascending to a level that puts that compartment into the decompression zone, a positive gradient is created and the compartment will off-gas or decompress (off-gassing = decompressing).
The closer a particular compartment gets to it's M-value line, the greater the pressure gradient that is created. Obviously, the danger is that if you off-gas/decompress too quickly, you will develop DCS symptoms and symptomatic bubbling.
This gradient is controlled by GF Hi% in Decoplanner. The higher you set it (up to 100), the closer these compartments are allowed to get to their respective M-Value lines.
This whole thing was a summary of what GF Hi% and GF Lo% do and how to interpret the tissue pressure graph. I am in no way a decompression expert, but I guess you realized that since you just read this..
Sorry Paul, I just found the question.[b said:Quote[/b] (Paul Oliver @ May 18 2003,19:38)]Peter where did you pick up the 2/3 rule, i quite like that.
good luck, whats for you, will no go past[b said:Quote[/b] (peter k @ June 01 2003,16:09)]I'm up at Aberdeen on Mon 9th June to be poked and prodded, so with a bit of luck I'll be back in at some point next week. To tell the truth, I'm shi**ing myself incase things go pearshaped.