SUUNTO DX - Manual (Page 121)

CAUTION
Always use the same personal and altitude adjustment settings
for the actual dive than for the planning. Increasing the personal
adjustment setting from the planned setting as well as increasing
the altitude adjustment setting can lead to longer decompression
times deeper and thus to larger required gas volume. You can
run out of breathing gas underwater if the personal adjustment
setting has been changed after dive planning.
10.2.2. Altitude diving
The atmospheric pressure is lower at high altitudes than at sea level. After traveling
to a higher altitude, you will have additional nitrogen in your body, compared to the
equilibrium situation at the original altitude. This "additional" nitrogen is released
gradually over time and equilibrium is restored. It is recommended that you acclimatize
to a new altitude by waiting at least three hours before making a dive.
Before high-altitude diving, the instrument must be set to the Altitude Adjustment mode
to adjust the calculations for the new altitude. The maximum partial pressures of nitro-
gen allowed by the mathematical model of the dive computer are reduced according
to the lower ambient pressure.
As a result, the allowed no-decompression-stop limits are considerably reduced.
10.3. Oxygen exposure
The oxygen exposure calculations are based on currently accepted exposure time
limit tables and principles. In addition to this, the dive computer uses several methods
to conservatively estimate the oxygen exposure. For example:
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