My son banned me from buying a PC because he said he didnt want his sleep disturbed by my late-night phone calls. I use a Mac, mainly because the designers of the operating system appreciate that there are customers out there like me.
Kevin Gurr obviously delights in computer wizardry but even he has come to realise that Steve Jobs was on to something when he decided to make home computers simple. The new VR Technology VRX is intended to be the Mac to the VR3s PC.

VRX and Gradient Factors
Kevin explained to me about the Variable Gradient Factors that are optionally used in the VRX, and I have tried to simplify things here without missing too much detail.
The human body cannot be precisely mathematically modelled, but this is what decompression algorithm writers attempt to do. A degree of belief in the theory will always be necessary. Haldane did some empirical studies at the start of the 20th century, since when ideas have been modified by the likes of Buhlmann, based on anecdotal evidence.
Haldane decided that human tissue could safely experience over-pressurisation during an ascent, and that the subsequent decompression profile should not exceed what has since become known as an M value.
As each theoretical compartment reaches this point, a decompression-stop is required.
When plotting tissue-compartment gas-pressure against the ambient pressure of depth, gradient factors add in a degree of caution by reducing the pressure gradient, and modify each M value by taking a percentage between M value and ambient-pressure value.
Richard Pyle, an ichthyologist, introduced a practical and easily understood solution with Pyle Stops, modifying the decompression profile to reduce excessive over-pressurisation at depths greater than traditionally thought.
Pyle allowed his faster tissues to off-gas before ascending to the first traditional stop-depth. This had the disadvantage of allowing slower tissues to on-gas during the process, requiring additional shallow stops.
Bubble models such as the VPM (Variable Permability Model) attempt to account for the growth phases of inert gas bubbles and their subsequent effect. In recent years these bubble models have been modified, but this is thought by some not to be a complete solution.
A major drawback of gradient factors is that they need to be adjusted to suit each depth and time exposure. An adjustment for an 80m dive may not suit a 30m dive.
Kevin Gurr believes that the new Variable Gradient Model (VGM) is the answer. It has the effect of padding out stops at certain deco points while reducing stop times at others, changing them automatically again for each different scenario while allowing a degree of user-input dependent on the application.
Its a new tool that combines in one approach much of what is known, and may predict some of that which is not.

The VRX comes fully loaded for both closed-circuit and open-circuit diving, and with the VGM algorithm. As such it has layer upon layer of menu options that can be quite confusing at times, as these are accessed by either long or quick pushes of either of the two buttons, or both.
It is also a multi-function instrument in that not only can you use it for extensive dive planning but also for calculations when mixing gases. The instruction manual comes in CD form, and I fear a lot of people will be using a lot of paper and ink to print out its almost-100 pages, as its not easy to scroll through in PDF form.

Display Legibility
People will inevitably make superficial comparisons with the VR3. The VRX is slimmer, less like something designed as ballast, and altogether more attractive.

In the Water
Despite its coloured display, unlike the VR3 I found the VRX quite difficult to read.
This is partly because small characters are used for some of the information, but also because the pyramid-curved face of the screen-protector reflected light in shallower water in a disruptive manner.
This made it impossible to photograph the display, too. It is backlit, so in the gloomy depths this is not a problem.
There is a whole lot of advanced thinking wrapped up in this dive computer, so go to the VR Technology website to get the full nine yards.
If you buy one of these instruments, it promises to be the only one youll ever need.

The VRX allows the user to plan almost any dive extensively, whether it be trimix, CCR trimix, CCR nitrox or even a simple single-tank nitrox dive. You can choose various degrees of caution by gradient factors variable by depth.
You can choose different approaches to decompression theory, too.


PRICE £1465 fully loaded
NORMAL IN-WATER DISPLAY Depth, remaining no-stop time, dive time, ascent-rate, deco stop time and depth, oxygen exposure
DIVE PLANNING Yes (including dive simulation)
MODES Nitrox/Trimix/Gauge/CCR
BATTERY Rechargeable
DIVER GUIDE width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100%