Necessity of a back up computer/watch for NDL diving

[markmud]

Thanks! Good to know. Im actually going to sell my Oceanics as I just bought a Shearwater Perdix AI.

Beat ya to it

I got mine last February.

cheers,
markm

 

[MargaritaMike]

Thanks! Good to know. Im actually going to sell my Oceanics as I just bought a Shearwater Perdix AI.

You can always keep it as a backup and dive with 2 computers. The money you get is probably less than the cost of a trip cut short. YMMV

Cheers -

 

[seeker242]

Thanks! Good to know. Im actually going to sell my Oceanics as I just bought a Shearwater Perdix AI.

I kept my Oceanic as the backup. But I don't ever use it except on tech dives and vacation trips.

 

[Steelyeyes]

Just remember a dive computer has no idea what is actually happening inside the wearers body, a backup computer only knows about the dives it has been on. If it is in your bag for half the trip then you have to do the 12 hour wait the same as if you were switching to tables.

Mine are both designed to be worn on the wrist. They're both part of my pre dive checks. Generally the backup and the primary have their wristbands buckled together when the backup isn't buckled around my left shoulder strap. It's not a backup if it's not in the water with you. If it's in the truck, boat, or dive bag it's now a spare.

 

[scubadada]

Hi Clayton,

With my Oceanics, there is default switch that can be turned off so the computer does not default to 21%. The 21% default is turned off on all of ours.

dive on,
mm

Hi @markmud

What Oceanic computer(s) do you have? I have many older Oceanic computers, Pro Plus 2s, VT3, Geo2, VT4. For all these computers, the FO2 remains as set until the computer turns off at 24 hours and starts a new dive series. When reactivated, it is on air and the FO2 must be reprogrammed.

All these computers have an often misunderstood FO2 50% Default. When off, it does nothing. When on, 10 minutes after the dive, the computer reverts 50% O2 for oxygen calculation and 21% O2 for nitrogen calculations. This requires that the correct FO2 be programmed for every dive, not just after a 24 hours of inactivity. I've not seen an Oceanic computer that does not require reprogramming the FO2 for a new series, but, I am not familiar with the newest computers in the Oceanic lineup.

Edit: it appears that the PPX and Geo4 may have done away with the FO2 50% default, but all the Oceanic computers appear to revert to air for gas 1 after 24 hours of inactivity and initiation of a new series.

 

[caruso]

All these computers have an often misunderstood FO2 50% Default. When off, it does nothing. When on, 10 minutes after the dive, the computer reverts 50% O2 for oxygen calculation and 21% O2 for nitrogen calculations. This requires that the correct FO2 be programmed for every dive, not just after a 24 hours of inactivity.

Isn't this the most annoying useless feature you've ever seen in a dive computer? I always turn it off when choosing initial setting along with audible alarms that are the second most annoying feature on dive computers.

 

[caruso]

I would take 2 computers on such trip myself. (Edit) What does not follow is that I need two computers because I can't accurately figure out my accumulated gas loading.

A human being using a depth gauge and tables cannot determine their accumulated gas loading as accurately as a dive computer unless a) they dive a perfectly square profile b) account for every single depth deviation during the dive or c) are like Rain Man.

 

[MaxBottomtime]

Or use depth averaging.

 

[caruso]

Or use depth averaging.

Since when is an average as accurate as the actual numbers.

 

[Bigbella]

A human being using a depth gauge and tables cannot determine their accumulated gas loading as accurately as a dive computer unless a) they dive a perfectly square profile b) account for every single depth deviation during the dive or c) are like Rain Man.

The best analogy I have to offer, for keeping analog gauges and tables as a back up, is the current generation's large inability to determine direction (just suggest that a particular location is due West, and watch eyes glaze over); that, and an increasing inability to read physical maps, after the wider use of GPS. This now also extends to the sheaf of tables in my dive bag.

Dive tables are clearly written; easy to understand; are rather conservative, as a rule; and I have used them professionally and recreationally, for twenty-five years before I even saw my first computer. I have yet to have to cancel a dive, after the failure of a ten cent o-ring in one of my old Suuntos . . .