Page 28
Doc. 13301-Tec-RevB (2022-05-25)
Technical Modes
Operating Instructions
5. Decompression and Gradient
Factors
The basic decompression algorithm used by this
computer is Bühlmann ZHL-16C� It has been modified
by the use of Gradient Factors that were developed
by Erik Baker� We have used his ideas to create
our own code to implement it� We would like to
give credit to Erik for his work in education about
decompression algorithms, but he is in no way
responsible for the code we have written�
The computer implements Gradient Factors
creating varied levels of conservatism� The levels
of conservatism are pairs of number like 30/70�
For a more detailed explanation of their meaning,
please refer to Erik Baker’s excellent articles:
“Clearing Up The Confusion About Deep Stops” and
“Understanding M-values”� The articles are readily
available on the web� You might also want to search
for “Gradient Factors” on the web�
The default conservatism of the system depends on
the dive mode�
For OC Rec mode the default conservatism setting is
medium (40/85)�
For OC Tec and CC/BO modes where some
decompression is presumed, the default is a more
conservative 30/70� The system provides several
settings that are more aggressive than the default�
Do not edit GF values until you understand the
effects.
Graph from Erik Baker’s “Clearing Up The Confusion About Deep Stops”
Pressure Graph: Gradient Factors
100% 80% 60% 40% 20% 0%
Ambient Pressure, absolute (increasing depth > )
Surf
ac
e Pr
es
sur
e
Linear function for
gradual change in
Gradient Factors
M-value
Gradient
C
ompartment inert gas pr
es
sur
e
, absolut
e
y
0
0
x
Ambient Pr
es
sur
e Line
M-
value Line
GF Lo
generates
first stop
GF Hi (surfacing value)
maintains safety margin
First
Stop
• A Gradient Factor is simply a decimal fraction (or
percentage) of the M-value Gradient�
• Gradient Factors (GF) are defined from 0% to 100%�
• A Gradient Factor of 0% represents the ambient
pressure line�
• A Gradient Factor of 100% represents the M-value line�
• Gradient Factors modify the original M-value equations
for conservatism within the decompression zone�
• The lower Gradient Factor value (GF Lo) determines
the depth of the first stop� Used to generate deep
stops to the depth of the "deepest possible deco stop"
• The higher Gradient Factor value (GF Hi) determines
the surfacing tissue supersaturation�