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NDL variation

PieM
over 5 years ago
Hello everyone,

I have purchased a Descent MK1 a few weeks back and passed my PADI open water and advanced open water with it.
I am loving it but before my deep dive (30m) I checked my NDL in the watch planner and it was different to my buddy's by 20 or so seconds, he also has a descent.

Since then I have been checking the NDL for 30m and it changes, for example 10 minutes ago it was showing 14:48 (30m, salt water, low conservatism, PO 1.4) and now it is showing 14:47 (my last dive was 5 days ago).

Does anyone know if the NDL depends on other parameter? Maybe the atmospheric pressure?

Thank you.
  • 0 over 5 years ago
    The 20 second difference was either a different Conservatism setting, or just different dive profiles leading up to that dive. That is normal between dive computers. The second part is probably just rounding, it is only 1 second difference.
  • 0 over 5 years ago
    Thank you Mark.

    All the settings seemed similar on both watches, also on my watch I have seen variation of 4 seconds and more on the same day.

    I have attached 2 pictures taken in the same room 22 minutes apart and you can see both the NDL and MOD have changed.

    Also, this is on low conservatism and is 5+ minutes less than the PADI tables, do you guys have the same NDL?

    Not sure what is the reason, have contacted Garmin and they say they are looking into it but the person that has been assigned to my case asked me what NDL is and where was it displayed on the watch.

    ciq.forums.garmin.com/.../1476470.jpg
  • 0 over 5 years ago
    Could it have to do with the current air preasure that changes...?
  • +1 over 5 years ago
    PieM As Milosherman mentioned, the change in the NDL you are seeing is most likely due to the change in pressure/elevation your Descent is reading. You can calibrate the altimeter on your watch to get the most accurate reading for your location and the NDL should change as well. If you believe there is another issue feel free to send me a pm so we can investigate it further.
  • 0 over 5 years ago

    See below the answer from Garmin support that clarifies it. It is indeed linked to the pressure / altitude. I guess to get the most accurate reading calibrating both the elevation and atmospheric pressure before diving could be a good thing.

    "Hello Pierre-Marie,

    The Max Operating Depth is more correctly the Max Operating Pressure. Foe example if a user is diving in Denver (1 mile above sea level), they will have a higher MOD than a diver at sea level, like Florida, because they can dive deeper before they reach  the same equivalent absolute pressure. The Florida diver has approximately an additional 1524 meter of air pressure on their back with is equal to 1.2192 meter of water depth.

    Why it varies, it is because the MOD and NDL will vary with ambient pressure. This is why you may see N2/He load be 1% on the surface interval widget even though you are not diving. For example, if a storm rolls through the ambient pressure drops, you would be technically over pressure and off gassing (a very small amount)."

    Happy and safe diving to all.