Paula, from the Gekko manual (if you have the manual check pages 35-36):
The dive computer can be adjusted both for diving at altitude and also to increase
the conservatism of the mathematical nitrogen model.
3.7.1. Altitude Adjustment
When programming the instrument for the correct altitude, you need to select the
correct Altitude Mode according to Table 3.4. The dive computer will adjust its
mathematical model according to the entered altitude mode, giving shorter nodecompression
times at higher altitudes (see Section 6.1. Operating Principles,
Table 6.1. and 6.2.).
The entered Altitude Adjustment Mode is indicated by mountain symbols (A0, A1
TABLE 3.4. ALTITUDE ADJUSTMENT RANGES
Altitude
mode
Symbol
on display
Altitude
range
A0
A1
A2
0 - 300 m [0 - 1000 ft]
300 - 1500 m [1000 - 5000 ft]
1500 - 3000 m [5000 - 10000]
= one mountain, or A2 = two mountains). Section 4.2.4. Personal Adjustments
describes how the Altitude Mode is adjusted.
Traveling to a higher elevation can temporarily cause a change in the equilibrium
35
of dissolved nitrogen in the body. It is recommended that you acclimate to the
new altitude by waiting at least three hours before making a dive.
3.7.2. Personal Adjustment
There are adverse personal factors for DCI which divers can predict in advance
and input into the decompression model. Factors that may affect susceptibility to
decompression illness vary between divers and also for the same diver from one
day to another. The three-step Personal Adjustment Mode is available, if a more
conservative dive plan is desired.
The personal factors which tend to increase the possibility of DCI include, but
are not limited to:
- cold exposure - water temperature less than 20 ¡C [68 ¡F]
- the diver is below average physical fi tness level
- diver fatigue
- diver dehydration
- previous history of DCI
- stress
- obesity
The Personal Adjustment Mode is indicated by a diver symbol and plus signs (P0
= a diver, P1 = diver +, or P2 = diver ++). Section 4.2.4. Personal Adjustments
describes how the Personal Mode is adjusted.
This feature should be used to adjust the computer to be more conservative,
according to personal preference, by entering the suitable Personal Adjustment
Mode with the help of Table 3.5. In ideal conditions, retain the default setting, P0.
If conditions are more diffi cult or other mentioned factors which tend to increase
the possibility of DCI exist, select P1 or even the most conservative P2. As a
result the dive computer adjusts its mathematical model according to the entered
Personal Adjustment Mode, giving shorter no-decompression times (see section
6.1. Operating Principles, Table 6.1 and 6.2).
TABLE 3.5. PERSONAL ADJUSTMENT RANGES
Personal
mode
Symbol
on display
Condition
P0
P1
P2
Ideal condition
Some mentioned factors
or conditions exist
Several mentioned factors
or conditions exist
Desired
tables
Default
Progressively
more
conservative
If you don't have a manual, here's a link:
http://ns.suunto.com/Manuals/Gekko/Userguides/Gekko_userguide_EN.pdf