Do you require it to be able to grow with your own expertise as you increase your knowledge and qualifications, diving with increased oxygen-content gas mixes, or maybe even close-circuit life-support systems
There are so many models on the market. Some offer very basic functions, others are more advanced and offer multiple functions.

Subgear, part of Johnsons Outdoor which also owns Scubapro, has a multi-function dive computer in its ever-growing range of dive gear, and sent me one to take under water and see whether it ticked any boxes.

The Hardware
The SG XP-3G is a capsule-style single-plastics module that fits into either wrist- or console-mounts.
The wrist-mount can be used with the supplied watch-style rubber strap or, by removing the securing pins, can be bungee-mounted using the four holes already in place around the mount base.
A standard CR2450 button battery that is user-changeable powers the 3G. It sits in an O-ring-sealed compartment with a screw-down cover..

A sacrificial clear-plastics cover protects the recessed screen. Two oversized buttons on the front face provide access to all the computer’s menus and functions.

The Software
The XP-3G dive computer is rated to a maximum depth of 120m and has the capability to pre-program three oxygen-rich gases (nitrox) from 21% to 100% O2 in 1% increments.
It uses the proven Buhlman ZH-L8 ADT MB adaptive algorithm, which is intended to increase safety and maximise bottom time by constantly adjusting the decompression plan during the dive, taking into account risk factors such as cold water, fast ascents or the potential for formation of micro-bubbles.
The multiple modes include Dive, Gauge, Apnea and CCR. Gauge mode displays information on current depth, maximum depth, time and ascent rates sampled at 4sec intervals.
Apnea mode displays the same information but adds alarms at intervals of depth or time and samples at quarter-second intervals for increased accuracy.
The CCR mode is designed to give dive information based on two PO2 set-points, and can be set to mimic those preprogrammed into your closed-circuit rebreather’s software. SP1
for the dive phase and SP2 for the deco phase can be set to a maximum of 1.0 or 1.6bar respectively.
In Dive mode the XP-3G gives all the essential information needed to conduct dives in safety. This includes current depth, deco depth, dive time, no stop time, ascent rate, water temperature and a safety / deco-stop timer.
The computer automatically adjusts to the current altitude by measuring the ambient air pressure before a dive.
The computer also has a digital-watch function complete with an alarm clock in
either 12 or 24hr format. Each dive is logged automatically in the computer’s memory, with 25 hours of profile storage at a 4sec sampling rate.
Logged dives can be downloaded to your desktop via clever infra-red data-transfer technology.
Between dives the surface interval and “wait to fly” times are displayed. These are committed to the computer’s memory every hour, enabling vital information to be saved if the battery fails or is replaced.

In Use
I took the XP-3G to the Canary Islands, and my first impression was of how easy it was to set up, using the two-button long-push, short-push system to access the menus.
A long push on the left button switches the unit on and displays all the digital graphics for a few seconds before going to the Surface mode screen.
A short push of either button opens the menu options, and further short pushes on either button scroll up or down the menu, while long pushes enter the menu options.
Under water a long press on either button switches on the backlight, and a short press accesses gas-switch options.
This might sound complicated, but in reality I found that the unit became intuitive to use very quickly. Digesting the instruction manual, a practice I wholeheartedly recommend, helped immensely.
The display has sharp black LCD graphics set against a green screen, and I found these easy to read even with my age-related sight deterioration.
Under water, all the essential information is displayed, and a quick look was all I needed to digest the information.
This enabled me to concentrate on the important things such as watching nudibranchs lay eggs, or marvelling at the flexibility of the numerous cephalopods found on the Atlantic reefs.

Here is a dive computer that has functions that can grow with your qualifications and experience. It can be used as a back-up to the onboard computer on a CCR or as a dive-timer in conjunction with tables for serious open-circuit technical diving.
It can be used with a default gas and two further enriched-oxygen gases for extended range or decompression nitrox diving or, in Apnea mode, can be a useful companion as you hold your breath and fin to the depths.
Otherwise it can be used as a no-nonsense, plain old dive computer, keeping you from overstaying your welcome at depth and ending up with an injury.
As a bonus, it will wake you in the morning so you don’t miss breakfast or rope-off times.
The real advantage is the price; at just under £260 this is an awful lot of technology in a flexible package that would suit 90% of all my diving needs.
Hats off to those SubGear guys – their clever and versatile dive instrument did indeed tick all my boxes.

PRICE £259
ALGORITHM Adaptive Buhlman ZH-L8 ADT MB
MODES Dive, Gauge, Apnea, CCR, Surface
GASES Three, switchable
NITROX 21-100%
UNITS Imperial or metric (changeable)
DIVE LOG Infra-red wireless data transfer to PC or Mac.
POWER CR2450 battery, user-changeable
WARRANTY 1 year, limited
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