Cochran COMMANDER, Owner'S Manual

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SALT/FRESH WATER COMPENSATION (High/Low
Water Conductivity):
There is approximately a three
percent difference in depth readings taken in salt
water versus fresh water. Some dive computers are
calibrated in feet of fresh water and some are
calibrated in feet of seawater. Diving in a medium
different from what the dive computer is calibrated for
will cause apparent depth errors. Only COCHRAN
dive computers, including the COMMANDER, actually
determine the type of diving medium and compensate
the depth reading accordingly. This is accomplished
by measuring the conductivity of the water during a
dive. Caution must be taken in interpreting this
reading since some apparent fresh water is actually
high in minerals or contaminants and is correctly
compensated as salt water (High Conductivity). This
commonly occurs in some caves, springs, and lakes.
ALTITUDE ACCLIMATIZATION: Driving or flying to
a dive site significantly higher in altitude requires
special modifications to the "sea level" algorithm. The
COMMANDER regularly samples the ambient
barometric pressure to determine these changes in
altitude whether the unit is On or Off. Accordingly, the
decompression algorithm is changed to reflect these
barometric pressure changes. Note that temperature
and weather systems also affect barometric pressure
and hence, apparent altitude. Using the Time-To-Fly
digits, the number of hours required to “adapt” to the
new altitude is immediately known to the diver. If a
significant altitude change occurs, a minimum of one
hour should pass before diving to allow the unit to
adapt to this new altitude. Rapid changes in altitude
should be avoided. The dive computer may interpret
a rapid change from a higher altitude to a lower
altitude as a dive. Should this occur, removing the
batteries for ten minutes will reset the computer,
however, all tissue nitrogen loading will also be lost.
Should it be desired to initiate a dive PRIOR to
completing the adaptation time, the COMMANDER
will treat this dive as a repetitive dive in its algorithm,
taking into account the "residual" nitrogen present due
to travel to altitude. There are two methods of
compensating for altitude. Via the Analyst
®
PC
Interface, ZONE or SEAMLESS altitude compensation
may be selected.
In ZONE all altitudes less than 2,000 feet above sea
level use the sea-level algorithm. At altitudes greater
than this, altitude compensation is “seamless”;
literally, every small fraction of gained altitude is