Features of dive computers


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 glance.
  • 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 lakes.
  • 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 chamber.
  • 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.





Updated July 1, 2002 3:55 PM by Vlad Pambucol