43
The IQ-600 is designed to help divers avoid such situa-
tions by presenting information and warnings regarding cur-
rent PO
2
levels and cumulative exposure to elevated PO
2
s. To
do so, however, the IQ-600 must be set to an FO
2
that accu-
rately matches the concentration of oxygen in the gas mixture
being breathed.
Similarly, the IQ-600 is designed to help divers avoid
decompression illness by providing No-Decompression Limits
(NDLs) or mandatory decompression stop information. Again,
to do so, the IQ-600 must be set in a manner that accurately
matches the concentration of nitrogen in the breathing media.
When it lacks this information, the IQ-600 will attempt to
protect divers by basing its oxygen- and nitrogen-exposure
calculations on a “worst case” assumption. This is, that divers
may be breathing a mixture containing up to 79 percent nitro-
gen, or up to 99 percent oxygen. This is what we are referring
to when we say that the IQ-600’s FO
2
setting is in “default.”
When and How FO
2
Default Occurs: One factor in deter-
mining if and when your IQ-600’s FO
2
setting will default is
whether you set it for air or Nitrox.
If you set your IQ-600 for air (an FO
2
of 21 percent), it assumes
that subsequent dives will be made using air as well. Thus, it
remains set for air, dive after dive, without defaulting.
If, on the other hand, you set your IQ-600 for Nitrox (FO
2
s
of 22 to 50 percent), the computer assumes that subsequent
dives may also be on Nitrox. Thus, to protect you from
accidentally diving a Nitrox mixture to which it cannot
accurately monitor, the IQ-600’s FO
2
setting will default
ten minutes after surfacing from any dive in which it was
set to an FO
2
other than air.
