The requirements of technical diving have for some time called out for a decompression computer to handle the complexities of multiple gas switching, trimix and nitrox breathing mixes and of course the increasing popularity of closed circuit rebreathers. The launch of the VR3 computer by Delta-P Technology Ltd. is an answer to this call and is the first computer readily available that will cope with all these complexities. It is targeted primarily at the trimix open circuit market and the rebreather market. A number of open circuit decompression computers are already available at a more modest price for the o/c nitrox diver, but none will allow a switch between open and closed circuit modes and the use of up to 9 breathing gases as the VR3 will.

Trimix divers are used to careful planning of the dive and cutting individual decompression tables for each dive using programs such as 'Proplanner' and 'Zplan'. The VR3 side-steps the need to cut tables for each dive and is a true multi-level decompression computer. It is based on the Proplanner software, written by Nick Bushell and marketed by Kevin Gurr and uses the Buhlmann ZHL16 model for decompression. Although the use of a decompression computer for technical diving will allow diving to be carried out with a greater degree of flexibility than was previously possible, it goes without saying that planning gas management is still essential to ensure sufficient gas is available to carry out the decompression penalties incurred. In addition back up decompression tables and a secondary dive timer must still be carried and used in the event of a failure in the decompression computer itself.
The VR3 comes in 4 models:

• Nitrox open circuit
• Nitrox closed circuit
• Trimix open circuit and
• Trimix open circuit and closed circuit.

As the only difference between these models is the software capability, lower models can be upgraded to a higher specification without the need to purchase a new computer. A copy of 'Proplanner' is provided with each VR3 sold, together with a copy of 'Prolog'. This enables a dive profile from a dive already carried out to be downloaded to a personal computer via an infra-red link. Tissue gas loadings can then be input to Proplanner to plan the next dive more accurately than the simple use of a rectangular profile.

The VR3 is ruggedly built with a hard-anodised aluminium case measuring 120 x 75 x 35 mm and weighing a hefty 500 grams. Two magnetic slide buttons on the front of the case control all inputs. By the use of a short button push or a long button push of either button or of both together, all the menus of the VR3 can be accessed and selected. The computer is turned on by a long push of either button. After a couple of seconds the start-up display appears and shows the owner's name and telephone number, which can only be input at the factory. This feature could prove useful if the unit was ever lost and found again (by a truly honest person !!). It also enables two identical units to be differentiated from each other. The start up display also shows the state of the batteries (two Lithium DL123 disposable camera batteries).

A button must be pressed within a few seconds to confirm that the VR3 is needed. This prevents accidental switching on and loss of battery life. After a few seconds the start-up display is replaced by the surface display showing the date time at the top of the panel. In the centre is shown the setpoint (for closed circuit rebreather diving), the breathing gas selected, the temperature and the depth of the shallowest decompression stop, which can be selected by the diver at 3, 4.5 or 6m. At the bottom of the screen are three input options. Pressing both buttons invokes the message 'Dive now'. This will leave the VR3 switched on in surface-mode for 5 minutes or until the pressure transducer detects water pressure, when it will automatically switch into dive-mode. If a dive is not commenced within 5 minutes then both buttons must be pushed again or the computer will switch itself off. I found this function a little disconcerting and more than once found that the VR3 had turned itself off before the start of the dive, when a descent did not begin as soon as expected. However, it can be turned on at any depth shallower than 6m without a problem and I quickly learned to check the computer at the start of every dive. The advantage of a manual switching system over the more popular electric contact system seen on many other computers is that the problems of unintentional battery drain when stored in a wet dive bag are no longer a concern.
Two other menu options are accessible when the VR3 is in surface mode:

• Gas - allows selection of breathing gases
• Opt - allows access to a range of other menu options

The Gas menu enables a switch between open circuit and closed circuit modes. In addition, up to 9 different trimix and nitrox gases may be input. A novel feature of the VR3 is that gases may be defined as 'active' or 'passive'. An active gas is one that will be used on the next dive. During the dive the VR3 will automatically advise the optimum gas to be used to minimise the decompression obligation. If the diver makes the gas switch recommended then a confirmation of this switch is needed by pressing a button to let the VR3 know what gas is being breathed. If for any reason the diver does not make the recommended gas switch then the VR3 will continue to calculate the decompression loading based on the current gas selected. Passive gases are retained in the VR3 memory but are not expected to be used on the next dive. However by the pressing of a sequence of buttons a passive gas may be turned into an active gas during a dive and then used. For example you may be using a 75% Nitrox mix but your diving partner has an 80% mix which can be input as a passive gas. If you have need to use the 80% Nitrox then it can be activated and used for decompression calculations.

Once the VR3 detects water pressure (and is switched on!) it will automatically switch into dive-mode. The current dive time and depth are shown in large figures. Beneath this the time to reach the no-stop limit is shown as a negative number. Once the dive goes into decompression, this figure changes to the depth and time of the deepest stop. Below this is seen the total time needed to ascend to the surface, the %CNS of oxygen absorbed and a reminder of the current breathing gas.

In the lower half of the screen is a message panel that is normally blank. When the VR3 wishes to communicate a message, it will appear here. For example if you ascend past a compulsory decompression stop then a 60 second countdown begins and the message 'Descend' appears. Failure to descend within a minute will provoke the message 'Use tables'. However, unlike other computers, the VR3 will not abandon you if its recommendations are violated. It will always give its 'best guess' of what you should do to avoid decompression illness, even though you may have accidentally strayed outside the envelope of the Buhlmann model.

All these features and flexibility come at a price and it's not a cheap one! The basic nitrox open circuit model retails for £799. The trimix rebreather model retails for £1099. However, having bought one VR3 computer you should never need to buy another. The VR3 is fully programmable and any updates can be made by returning it to the factory.

Delta-P Technology will need to be satisfied that would be purchasers are suitably qualified at the right level of diver training before selling the requested computer. Find out more from the website: http://www.VR3.co.uk or by calling 01202-870570

Review by Steve Millard