Dive Computers and Software

On the basis that my first dive computer did not need to cover technical diving and with a limited budget I looked for a simple unit which could store a number of dives and was able to recall these for later analysis. I finally chose (rightly or wrongly) the Mares Tutor. This is an entry level unit which has all the basic features and few extras for around £150.

The Tutor has a clear display with all information being available in dive mode on the screen. It does have pushbuttons rather than metal contacts to select the various modes of operation - no more licking fingers just to get to the data. It is powered by a standard AAA battery which can be easily changed by the user.

The Tutor can be switched on by pushing the mode button or automatically by entering the water. In manual switch on mode the Tutor does a self check autozero procedure (automatic calibration) and checks battery level. In the water the Tutor switches on automatically, If the unit is not taken to 1.5m within three minutes it switches into wait state. Beyond 1.5m it automatically enters dive status and records depth, time and average temperature.

The clear display shows current depth, dive time, remaining no-decompression time and temperature. Rate of ascent indicator is also shown as a percentage of current depth (shown by bars at 60, 90, 100, 120%. The allowed ascent rate varies with depth from 18m/min (90 - 20m) 12m/min (20 - 10m) and 10m/min (10 - 0m). An audible warning is given if the predetermined ascent rate is exceeded by 20%, this is very easy to set off at shallow depths simply by moving your arm too quickly. A safety stop of 3 min is also signalled during ascent between 3.5 and 5m. Depth control is important here, if you drop your arm below the 5m level the stop automatically resets to 3min, quite annoying until you realise what is causing it.

After the dive the Tutor shows 'No Fly' time which is reset to 12 hours with no decompression diving or 24 hours with decompression or repetitive dives. Surface interval is also shown together with any UBA asterisk symbols that give a warning of any specific errors hence the name 'Tutor'. These are a little basic and can be triggered by arm movements especially at shallower depths. The theory is good however, if your diving attracts no symbols this means good dive profiles, while getting more symbols should show any particular problem areas and help you learn to dive more conservatively.

Setting is very straightforward using the mode switch, date and time, three levels of altitude setup, units for temperature and depth are also available. It is also possible to override the automatic STOP setting after uncontrollable ascent by setup menu, this could be useful during training exercises etc. to avoid the computer locking up.

The last 20 dives are held in memory together with profiles for the last 10 dives. This information can be accessed on screen or transferred via an optional interface to a PC. This PC interface sounds like an excellent idea until you discover that it costs another £150 which does limit the idea of a budget dive computer in my book.

It is possible however to view the data in one minute increments for the last 10 dives. Armed with this knowledge you can input these into a simple spreadsheet while reading the dive profile data on screen. I made an Excel spreadsheet with an embedded graph which does the trick nicely. A copy of this is available below for information. To save keying in minus values for depths these are automatically converted to the correct sign on entry. I saved the basic sheet with no data and then resave each dive in numerical order. I will probably develop this in the future to include more details about divesite conditions, equipment etc. The principle can be adapted to other dive computers with profile display without spending the additional money on an interface which is limited to one model. Hopefully this could save money in the long term until the next super wizzbang dive computer comes along.

I made over 100 dives with the Tutor. This has been a very good tool but having certified for Nitrox diving I wanted a computer which could be used for different oxygen percentages which still gave me the same benefits as diving with the Tutor. Again, I studied the diving press and made enquiries of other divers, both face to face and via internet newsgroups. I considered gas-integrated computers which can be fitted to the high pressure hose or receive their information via a radio pressure transducer mounted on the first stage. The addition of cylinder pressure does allow more precise calculation for example including gas remaining and I was very keen on the Suunto Cobra which fits on the end of the HP hose. A drawback of this is that if it packs up for any reason there are no back-up pressure or depth analogue gauges for safety. The radio transducer type gets around this problem but the prices were too high for my budget.

I chose the Suunto Vyper because it had the features I was looking for and a reasonable price tag. It also had a safety profile which seemed close to that of the Tutor. I particularly liked the way it recommended a three minute safety stop at the end of the dive. The PC interface was also readily available and Suunto allowed their dive logbook software to be downloaded from their web site so it could be checked prior to buying. They also had a complete operation manual in Adobe Acrobat pdf format which was available for download so you could see exactly how the various modes were used before making the investment.

The Suunto Dive Manager software is very easy to use and does allow the dive profiles to be recorded and displayed on the PC. There extensive facilities to allow the user to annotate each dive and once a particular entry has been made (dive site name, buddy etc.) this appears as a drop down menu box to save having to re-type the infomation again in the future. The only drawback is that every new entry is checked with a dialog box which ask you if you want to save it, I wish this could be disabled by software preference setting but maybe this will come with a future release.

The tissue loading is shown at each stage of the dive as a series of compartment bar graphs which is useful when reviewing a dive. By moving the cursor across the profile, the values change and this gives a good chance to see the mathematical model originally developed by J S Haldane in action. Suunto call their mathematical algorithm a Reduced Gradient Bubble Model or RGBM which uses 9 tissue compartments from 2.5 to 480 minutes. The compartment M values are tracked up to 100 hours after a dive. This is said to allow tracking of both disolved and free gas in the tissues of divers performing a wide range of manouevers. This model is said to be able to address a number of circumstances outside the range of simple dissolved gas models, particularly continuous multi-day diving, closely spaced repetitive dives, accounting for diving deeper than previous dives etc.

The default recording interval is 20 seconds but this can be adjusted by the user to 10, 30 or 60 seconds with the PC interface. A higher sampling rate uses more memory and means that fewer dives can be stored on the computer. The memory capacity at 20 seconds is around 36 hours of diving.

User settings are provided for Air, Nitrox or Gauge modes. Altitude adjustment and personal adjustments are also provided, it is also possible to set alarms for dive time or maximum depth. A backlight is provided for low light conditions and a bookmark facility allows the user to annotate the dive at particular points of interest. The display is clear and makes good use of the information displayed. In Nitrox mode, for example, the display shows current depth, maximum depth, Oxygen %, No Dec time, temperature and elapsed dive time, a bar graph also shows oxygen loading factor OLF. If the oxygen loading exceeds pre-determined amount (default setting 1.4 ppO) an alarm will sound.

In summary, the Suunto Vyper is a good choice for a variety of diving conditions. I am still using the Tutor for back up and have no regrets learning to dive on this cheaper unit before upgrading. Individual choices will vary and you need to make sure that you have the right unit for your particular style of diving. I beleive that it is not adviseable to spend too much at first then end up with a computer which will be replaced after a couple of years anyhow. My Tutor gave excellent service over three years and more than 100 dives and would still recommend it as a good first choice. Technology does move on however and you need to look hard before jumping too quickly. Listen to the advice of others but do make your own decision when your needs are clearly met by the computer of your choice.

Return to Main Menu