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Necessity of a back up computer/watch for NDL diving

Discussion in 'Computers, Gauges, Watches and Analyzers' started by Divectionist, Mar 12, 2019.

Do you generally wear a backup device?

  1. No

    50 vote(s)
  2. Yes, a watch

    19 vote(s)
  3. Yes, second dive computer

    67 vote(s)
  1. markmud

    markmud Self Reliant Diver ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: South Lebanon, Ohio
    Beat ya to it :cool:

    I got mine last February.

    MargaritaMike likes this.
  2. MargaritaMike

    MargaritaMike Divemaster

    # of Dives: 1,000 - 2,499
    Location: On a non-divable lake in SE Texas
    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 -
    Clayton122 and markmud like this.
  3. seeker242

    seeker242 DIR Practitioner

    # of Dives: 200 - 499
    Location: Pompano Beach, FL
    I kept my Oceanic as the backup. But I don't ever use it except on tech dives and vacation trips. :)
    Clayton122 likes this.
  4. Steelyeyes

    Steelyeyes Barracuda

    # of Dives: 200 - 499
    Location: Redmond Wa
    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.
  5. scubadada

    scubadada Diver Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Philadelphia and Boynton Beach
    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.
    markmud likes this.
  6. caruso

    caruso Manta Ray

    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.
    scubadada likes this.
  7. caruso

    caruso Manta Ray

    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.
    Steelyeyes and markmud like this.
  8. MaxBottomtime

    MaxBottomtime Solo Diver

    # of Dives: 1,000 - 2,499
    Location: Torrance, CA
  9. caruso

    caruso Manta Ray

    Since when is an average as accurate as the actual numbers.
    markmud likes this.
  10. Bigbella

    Bigbella Nassau Grouper

    # of Dives: I'm a Fish!
    Location: San Francisco
    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 . . .

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