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Altimeter auto calibrate?

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  • Altimeter auto calibrate?

    The VA HR altimeter sensor can be manually calibrated, which I regularly do. However, I also have the auto calibrate option enabled, but... what does that do? I would expect it calibrates the altimeter sensor based on gps data of your location? But, that almost never works. E.g. I walked for 40 minutes today with GPS enabled. But when I look at the current altimeter value it says 425m. But, my current location is at 23m. That is more than 400m off.
    So... what does auto calibration do/mean?

  • #2
    I don't know the VA HR, but my Garmin watch will only do an autocalibration if I get a reliable GPS fix (indicated by a green ring at the screen perimeter) before I press Start.

    If I press Start and then afterwards get a GPS fix, the watch will not autocalibrate.

    I don't know if that could be your problem?

    Also, make sure not to test this by manually calibrating your watch to a wrong altitude and see if the auto calibration will correct it. Your manual calibrations will be remembered and will in two distinct cases be trusted more than the GPS altitude (or at least on my watch they will):
    • If you did a manual calibration very shortly before starting the activity, no matter if the watch knew your GPS coordinates at that time.
    • If you did a manual calibration in the past at the same location, and the watch knew your GPS coordinates at that time.
    Last edited by AllanOlesen67; 03-13-2018, 03:54 PM.


    • #3
      I always wait for a GPS fix before starting an activity and I normally only calibrate it manually at home (always on 23m). Last time I calibrated it manually when I was not at home I was on the starting grid of the Spa Francorchamps circuit in Belgium, which is on 418m and 120km away from home.


      • #4
        When you kick off a GPS activity the VAHR should calibrate the altimeter to the GPS altitude if auto is selected. Usually not super accurate, but reasonable.

        Sounds like it isn't auto calibrating properly.

        Try using Glonass instead of GPS. Hold start> setting> Apps> select the App and in its settings menu (providing it's a Garmin default app) you'll find GPS ON and inside is the Glonass option. Glonass is more accurate in the vertical plane, I find. But that may not always be the case and it's a matter of try and see it it works better for you. Glonass will deplete your battery faster when in GPS based activities, but I don't find it significant, and therefore it isn't problematic.

        This could also be a firmware issue (In my opinion v4.30 has lots wrong with it) some of it can be fixed by the following:

        1. Have you tried powering down and switching back on and trying again.
        2. Try a hard reset.

        Then try GPS again.


        • #5
          I already have Glonass enabled and also recently did a factory reset (about 2 months ago).

          I think it will auto update to altitudes on known locations (e.g. where you manually calibrated earlier). But, what is the bes5 method to manually calibrate? Do you need to get a GPS fix first and then go into the settings and manually calibrate? Or, can you go directly into settings and manually calibrate. I have been using the last method all the time, but maybe this is not correct so also the auto calibrate is not working as it should?


          • #6
            There are more types of auto calibration. The simple one where the watch just uses the GPS altitude will work without any previous manual calibration.

            But the auto calibration where the watch reuses an earlier entered manual altitude is different. This will require that the watch knew its location at the time where it was manually calibrated. Otherwise it has no way to know if it is at the same location the next time you start an activity there.

            Consequently, your first method is the one I use on my Fenix 3.

            For your second method to work, the watch would need to know its location from earlier GPS usage and be able to judge whether it had been moved to another location since then. I have actually seen some behaviour in my Fenix 3 which indicates that it may be doing such judgments. However, I would not rely on it.