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Does computer PLAN mode consider CNS limit?

Discussion in 'Advanced Scuba Discussions' started by nohappy, Sep 9, 2017.

  1. nohappy

    nohappy Angel Fish

    When we set our computer with nitrox setting and switch to PLAN mode before a dive, does it consider CNS limit along with NDL? I checked some of the popular computer manual, they all mentioned NDL only. I just wonder if it accumulates CNS clock. Or is that we can only get our CNS clock during diving?
  2. tep

    tep Barracuda

    # of Dives: 50 - 99
    Location: San Diego CA USA
    Check your computer's manual.

    I would hope that all Nitrox-capable computers would work this way, but check the manual for YOUR computer.

    I know that the Aeris Atmos2, which is a many years old model, considers oxygen toxicity (CNS) in its dive plan mode. See page 46 for an example.
  3. nohappy

    nohappy Angel Fish

    Thanks tep!
    That's useful. I checked sunnto d4i, deepblu, cressi leonardo manual, they didn't mentione oxygen in PLAN mode. So I just wonder if that means they don't consider it in PLAN mode (before diving).
  4. dbnewton

    dbnewton Manta Ray

    # of Dives: 500 - 999
    Location: United States
    You made me think. I am using Perdix AI. It wasn't obvious in the manual for nitrox. But I found it in the operations manual. https://www.shearwater.com/manuals/Perdix-Operating-Intructions-Manual.pdf

    Page 52:
    "Note: Residual tissue loading (and CNS%) from recent dives will be used in calculating the profile. "

    Since I also carry a Suunto Gekko as a backup I looked there as well. Same answer: yes

    See: https://www.simplyscuba.com/pdf/ScubaManuals/DiveComputers/Gekko Manual English.pdf

    Page 18:
    The Planning mode also accounts for the following information from previous dives:

    • any calculated residuial nitrogen

    • all dive history for the past four days

    • oxygen toxicity (Nitrox mode)
    nohappy likes this.
  5. scubadada

    scubadada Diver Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Philadelphia and Boynton Beach
    There are 2 major algorithms to monitor O2 exposure. The Seiko Epson algorithm includes a 90 minute O2 elimination half life in the calculations and is more liberal. The Pelagic Pressure Systems uses a rolling 24 hour exposure that is more conservative and is consistent with the NOAA guidelines. I am easily able to exceed the NOAA guidelines with 4 dives per day, 5 dives in a 24 hour window, using the NOAA guidelines, when doing my 4 dives per day using EAN36 in SE Florida. My O2 exposure is clearly taken into effect when in the planning mode on my primary VT3 or my previous backup Geo2. When applicable, O2 exposure dictates dive time rather than NDL. I have abandoned by Geo2 backup in favor of a Dive Rite Nitek Q, to learn Buhlmann with GF. the Nitek Q runs the Seiko Epson algorithm. It is in the best interest of all divers to understand how their computer works and how that effects the information available to them during the dive.
    nohappy likes this.

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