Unwrapping my post it felt like Christmas was coming again as I tore into the packaging to reveal the Buddy Nexus Dive Computer from AP Valves. This computer is a result of more than 18 months collaboration between Finnish Company Benemec and AP Valves.
I had first tried the early prototype Nexus a year before diving around the Manacles in Cornwall and found it a hardwearing useful dive computer with plenty of potential for the Nitrox diver. I now had in my hands the final retail version ready to be put through its paces.
The first thing that struck me was how well the Nexus was going to coordinate with my Buddy Inspiration Rebreather with it’s bright yellow front and black back and very cheerful yellow strap this was a change from the original drab black box tested in the prototype days. The strap is plenty long enough to fasten around even the bulkiest of dry suits, remove the strap and the unit will fit into the place of a standard depth gauge on your console. Included is a natty little carrying case and a couple of self-adhesive LCD lens cover screens. Also accompanying the computer is a comprehensive and well laid out Instruction Manual that had me up and running in a few minutes. An extra to be available from AP Valves is a PC interface that allows you to download your dive profiles and store them in the electronic logbook.
So what is so special about the Nexus? Firstly, it is a fully functioned two mix Nitrox dive computer aimed at the Nitrox and Extended Range technical diver offering the use of a bottom gas with a user programmable Oxygen content of 21%-50% and the use of a decompression gas range from the current bottom gas setting up to 100% Oxygen. Fairly standard for the modern dive computer market, but where the Nexus truly excels is the ability to switch the unit into Closed Circuit mode, where the unit has the ability to calculate your decompression, based on the constant Partial Pressure of Oxygen available with a Closed Circuit Rebreather. Rather than a Constant Fraction of Oxygen as with “normal” Nitrox computers. The significant advantage gained here is considerably longer “no-stop” times than those available from the fixed Nitrox tables or other Nitrox computers. For the technically minded the Nexus uses a modified Buhlmann type dive calculation model with eight tissue groups and 480 minutes half times.
Another attractive feature of the unit is the user changeable batteries, which are isolated from the main electronics and accessible by removing the four screws on the base of the unit. Battery life is a claimed 300 hours of dive time or about 15% less when the LED backlight is used. This level of battery performance is maintained by a clever built in revival routine. The display is laid out in a clear logical manner. All of the relevant information like depth, time and no stop are in prime position and large characters.
Sitting down with the manual I started to review the Open Circuit Mode settings first. Deciding to enter a bottom gas of 28% Oxygen content and a decompression gas of 50% this would enable me to compare the results from the computer against my standard accelerated decompression tables. Entering settings into the Nexus is a fairly simple task relying on the three metal contacts on the face of the unit. Bridging the contacts in the appropriate order allows the settings to be easily changed and confirmed. Entering the gas mixtures you also have the option to have the gas switch occur automatically at a chosen depth. It also possible to override the gas switch during the dive for example if you were to lose your decompression gas and have to continue on your bottom gas. An interesting point to note here is that when the unit powers down both of the mixture settings automatically default back to 21% Oxygen. This is a feature left over from Benemec’s involvement in the US market. On the closed circuit side once the settings are stored they stay that way until manually changed again. So for closed circuit diving you just strap it on and go. It is important therefore when diving in open circuit mode that you verify you have the correct values programmed in to the Nexus prior to starting the dive.
Switching the unit into Closed Circuit Mode is once again a simple matter of entering the programming mode using the contacts and changing the settings. Once in Closed Circuit Mode the user is then presented with a new set of options relating to the rebreather. The first being the entry set point of the unit then the diving set point and at what depth the change of set point should auto occur. You then enter the depth at which you want the set point to return to the entry setting on the ascent. Next you are presented with the option to have the set point changes occur automatically or manually. As with the Open Circuit settings the automatic set point change can also be overridden in water. Further manipulation of the contacts reveals the log book mode, pre dive prediction mode which will present no-stop times based on your current level of saturation and the current set point or Nitrox mix. Scrolling further on you enter into full dive simulator that allows you to run what if scenarios.
Taking the unit diving for the first time on Open Circuit was to be an Extended Range dive of 40m for 25 minutes with a 28% bottom mix and a 50% decompression mix. Taking along a Cochran commander programmed to the same gas mix and switch as a reference point and a set off tables cut using Zplan off we went diving. Throughout the dive the Nexus provided clear concise information and virtually matched the Cochran for stop times and cut two minutes of our hard tables. Visibility on this dive was very limited and one criticism of the Nexus I do have is the LED display lighting. I found the display a little difficult to read in very lowlight conditions despite activating the light.
The next dive was to be done in Closed Circuit Mode again to 40m using my Inspiration Rebreather. I easily changed the settings on the unit to reflect my 0.7bar entry set point and an auto switch at 15m to 1.3bar. Taking along my Cochran Lifeguard computer as a reference we entered the water. Descending down to 15m I raised the set point of the unit 1.3bar seeing the Nexus had also auto changed at the preset depth I continued my descent. Throughout the dive the readings from the Nexus matched the output from the Cochran. As we started the ascent after 25 minutes of bottom the Nexus gave me a 5-minute stop at 3m a minute more conservative than the Lifeguard. As is our normal practice we completed the stops at 6m, which presented no problem to the Nexus. On clearing my decompression penalty I also took this opportunity to test the manual override of the automatic set point change, tapping the unit three times overrode the planned auto set point changed and returned the unit to 0.7bar, a useful feature in multilevel dive profiles.
Having taken the unit on several deeper dives after the initial test we discovered that the inbuilt depth limitation on the display is approximately 65 meters however on returning to shallower depths the display returned and the unit continued to calculate the profile. Another possibly attractive feature is the manufacturers claim that the unit is apparently impossible to make sulk. If you abuse it, it just keeps on calculating!
In conclusion the Nexus is an attractive fully featured dive computer that will appeal to all levels of Nitrox diver from entry level to Extended Range, Closed Circuit Rebreather owners and those currently on Open Circuit but planning the switch to Closed Circuit. If I had to find something to complain about the only thing I could find was the poor backlighting. At a RRP of around £350.00 the unit makes a good investment, along with the PC interface retailing at around £79.00.
Silent Diving Systems can supply the Nexus and PC interface in North America, Central America, the Caribbean and terrotories with a retail price of $599.00 US and $119.95 respectively.
