In Time mode you can set day, date and time, in US or UK formats and, using 12- or 24-hour notation, set a variety of alarms.
You can even display two time zones if travelling, so the daily call home can be timed to cause minimum annoyance.
This is a two-gas – air and nitrox – computer, so will more than cover the diving requirements of most divers, few of whom use more than one gas-mix per dive. You can pre-set depth and time alarms, or switch them off, turn deep stops and safety stops on and off and lots more, customising the Geo4 to suit your style of diving, and can use it as a back-up in Gauge mode or to monitor your freediving.
Download the free DiverLog+ app and you can sync your phone or other mobile device to your Geo4 via Bluetooth and make all your adjustments from your device, as well as downloading dives for logging.
I did this, and it works very well, but once I had the computer set up as I wanted it I found it easier and quicker to adjust gas-mixes using the buttons on the computer. Being somewhat Luddite, I found that immensely satisfying.
You can set gases containing from 21% to 100% oxygen, so a bottom gas of air and a deco gas containing a higher proportion of oxygen is easily managed.
I used the Geo4 on a Red Sea trip, monitoring deco status for a single back-mounted 12-litre cylinder and then as a two-mix unit, when I supplemented that with a second bottle clipped as a stage and containing a richer nitrox mix.
It was easy to integrate setting the computer with checking the gas(es) in my tanks, adding very little to the pre-dive testing time.
In the water the data provided was very clear and easily read. My second reservation about watch size units is that the numbers can look weeny at a glance, but this display was clearly legible, with all the info you need and nothing you don’t.
Stray into mandatory deco and the display remained equally easy to interpret and use, with enough information to allow full control of the dive and the stops.
And, not being gas-integrated, you also need to be that bit more aware of what you’re doing and the gas supply remaining, something I prefer.
Gas-switching was a simple two-button process you can’t trigger by accident, and you can switch to either pre-set mix, provided the gas to which you’re switching is suitable for your current depth, as determined by the oxygen content and maximum allowable partial pressure you’ve set.
Switching back to your other gas is equally easy, if required, and an icon at the bottom of the screen tells you which gas the computer believes you’re breathing, so that you can check that you’re both on the same dive-plan.
Basic dive data for the Rosalie Moller wreck dive from the DiverLog+ app.
On the subject of mandatory deco, the Geo4, like other Oceanic computers, offers a choice of two deco models, one more conservative than the other. Oceanic says that the DSAT model is based on the same data used in the PADI RDP and will impose restrictions on repetitive deco dives, while the Pelagic Z+ algorithm is Buhlmann ZHL-16c-based and more conservative overall.
Some very basic tables at the back of the Geo4 manual compare the two. The manual also suggests that Oceanic doesn’t recommend deep stops on decompression dives, which is where current deco theory seems to be headed.
Geo4 graph from the dive on Rosalie Moller. It changed from blue to red when the dive moved into mandatory decompression, and the blue line is a gas switch.
Once you’ve selected an algorithm and made a dive you’re locked into using that algorithm until 24 hours after the final dive of your series, so you can’t change your mind midway through a liveaboard week, for example.
Not that I can see why you would. With either option you can choose to add extra conservatism into the settings.
For the record, I used the less-conservative DSAT model with no additional conservatism factored in, deep stops off and safety stops off.
I like my computers set to the bare bones of what will get me to the surface safely, and then to add in some padding myself, typically extending the shallower stops.
When we made three repetitive deco dives on the Rosalie Moller, the Geo4 gave me the stops I expected. I’ve dived that wreck a lot, so I’m pretty much dialled into the sort of deco likely to be required, and the Geo4 dished up no surprises.