Whichever computer you choose should be governed by the type of diving
you are doing. Price should not be your least concern as this can become
a critical component of your dive gear. Reliability, durability and accuracy
come at a price and you will thank yourself for choosing to get what you
need and not necessarily what you can afford.
- User replaceable batteries - cheaper to operate and if you
are diving away from home, you can bring spare batteries with you. Keep
in mind that if the batteries in a dive computer fail and you have already
done some recent repetitive dives, this residual nitrogen info will
be lost during the battery change. It is recommended that you cease
diving for 48 hours if you change the batteries under these conditions
so that upon recommencing diving, the computers residual nitrogen data
will be fairly accurate for your body's physical state
- Sturdy housing - some computers resist pressure through the
use of oil filled interiors. The housing though for these units are
fairly weak and can be damaged through impact. Housings that resist
water pressure through the strength of the housing tend to be more rugged.
However all computers should be treated with care as they were not meant
to be tossed around
- Large displays - computers display a lot of information in
a compact display. The larger the display, the less cluttered the display
of readings and the easier to view the readings. When under the effects
of narcosis, large displays are much easier to read especially at a
- Color coded readings - some computers show numeric values for
readings as well as a color coded bar graph for stuff like nitrogen
absorption and air pressure. These bar graphs tend to be easier to read
than numeric readings especially with the color coding.
- Decompression algorithm range appropriate to your dive profile
- some cheaper computers use a standard algorithm that ends at moderately
deep limits. However deep trimix or heliox divers doing decompression
may opt for a computer with a very deep algorithm. Computers taken beyond
their algorithms max depth will result in the computer switching to
gauge mode and not returning decompression status information
- Nitrox compatible - some computers allow the diver to dial
in nitrox mixes. They will then alter their estimate of decompression
status for the mix and also return oxygen exposure readings and exceeding
max depth for the mix warnings.
- Multiple gas mix decompression compatible - most nitrox computers
are quasi-tech computers and very advanced recreational units. Serious
deep technical diving involves the use of multiple mixtures of breathing
gases. At each gas switch, the computers algorithm would have to adjust
in order to remain fairly accurate. Some computers can handle 2 or more
gas switches. However most nitrox compatible computers assume that the
gas mix you dial in is what you will be using through the entire dive.
These computers therefore will give you faulty readings if you are using
multiple gas mixtures.
- PC downloadable - some computers can transfer the recorded
information to an IBM PC. The software can then keep a record of your
dives which includes dive profiles of each dive. This information is
useful for serious technical divers who want to analyze each step of
their dive profiles.
- Auto-activation - some computers automatically activate upon
contacting salt water. These computers have electrodes on their surface.
Current that passes through the completed circuit (electrode to water
to electrode) then triggers the device. Other computers require the
diver to physically activate them on the surface at which point they
will self-calibrate and then go into standby mode waiting to be activated
by increasing water pressure. Auto-activated computers are great for
divers who occasionally forget to check to see if their computer is
on because a manual activated one that has not been activated, requires
the diver to surface in order for the unit to turn on, calibrate and
then become ready to operate. On the other hand some users have difficulty
retrieving data from auto-activated units because data is retrieved
by licking ones fingers and completing the circuit between specific
electrodes. The manual activation computers though are easier to get
information out of because there are 1 or 2 buttons to push in order
to query the unit.
- Backlighting - backlit units tend to be more useful during
night dives or deep dives (where sunlight does not penetrate). These
units allow viewing without the use of lights which avoids the risk
to momentary blindness from the glare of dive lights reflecting off
of the face of the computer. Keep in mind that the use of backlighting
also increases the rate of battery drain.
- Audible warnings - some computers will give audible beeps when
the computer registers warnings or violations. These can be useful to
inattentive divers who infrequently check their gauges. However neoprene
hoods tend to muffle the sound of these audible warnings. Audible warnings
that continue to beep also tend to drain batteries much quicker than
if the unit is set to operate silently.
- Metric or imperial units - some computers can be switched to
read either units. This feature may be useful if for example a travelling
tech diver doing decompression is loaned a deco table in units that
is not normally what they use. To illustrate a Canadian diver who is
used to reading depth in feet, travelling to Switzerland may get a hold
of a metric deco table. Without being able to convert the readings in
this situation can make a decompression profile rather difficult.
- Full decompression obligation information - some computers
will only tell you where to stop and when to go to the next stop. These
computers do not give the diver any indication of how long they have
to remain at the stop. This can be unnerving as a diver has no clue
if their air will run out before their obligation is complete. Other
more expensive units may use a bar graph or numeric time indication
of how long a diver must remain at a given deco stop. This type of computer
is more useful in terms of determining the total decompression obligation
for regular decompression divers.
- Altitude algorithms - some computers will adjust to take into
account altitude for divers who do a variety of diving including mountain
- Fly time timers - most computers will display a countdown timer
from the time of your last dive to the time when it should be okay for
you to board a plane.
- Multiple languages - this is more a frill than a required feature.
However if you have visiting friends from another country who wish to
use your computer, the multi-language capacity can be a useful feature.
- Multiple dive day logging - some computers can save the information
from more than one dive. However only some computers can record the
dive information from more than one day. For example non-multiple dive
day logging computers used on a second day of diving will erase the
dive profiles of the previous day's diving and replace this info with
the current profiles. Only the residual nitrogen information will be
retained over multiple days of diving in this kind of unit.
- Multiple tissue compartment models - computers monitoring more
tissue compartments will generally be more accurate in decompression
status estimates than computers that only follow a few compartments
- Conservativeness - it is difficult to say for certain which
computer is more conservative than another but I have seen first hand
that my computers tend to be more aggressive than my buddy's computer
given a specific dive profile. However, conservative is good because
it is best to spend less time underwater and be able to return another
day than to spend more time underwater and end up in a recompression
- Individual coded transmitters for hoseless air integrated computers
- if a hoseless computer cannot be set to identify a specific pressure
transmitter, the use of more than one of this kind of computer may result
in cross talk between transmitters and computers. This obviously would
result in the display of faulty information.
There are some other features that computers will offer but for the most
part the above ones are key ones to look out for when selecting a computer.