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The no-decompression limits in the U.S. Navy tables are based upon six theoreti-
cal compartments for single dives, and one compartment for surface intervals and
repetitive dives. If you are familiar with table theory, you may know that they are
characterized by half times (i.e. the time required for 50 % equilibration to a pres-
sure change) ranging from 5 minutes to 120 minutes.
The Spyder includes the same six compartments, and three additional compart-
ments for an increased range of the mathematical model. The calculations are based
on all nine compartments for all phases of diving, including surface intervals and
repetitive dives. The Spyders half times range from 2.5 to 480 minutes.
Altitude Diving
The atmospheric pressure is lower at high altitudes than at sea level. After travel-
ing to a higher altitude, the diver will have additional nitrogen in his body, com-
pared to the equilibrium situation at the original altitude. This additional nitro-
gen is released gradually in time and equilibrium is reached within a couple of
days. Do not dive until the equilibrium is reached.
Before high altitude diving the Spyder must be set to the high altitude diving mode
to adjust the calculations for the new altitude. The maximum partial pressures of
nitrogen allowed by the mathematical model of the Spyder are reduced according
to the lower ambient pressure.
As a result the allowed no-decompression limits are considerably reduced.
Surface Intervals
The Spyder requires a minimum surface interval of 10 minutes between dives. If a
surface interval is shorter than 10 minutes, the Spyder dive counter and dive timer
