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Altimeter – continuous calibration

simonjharris
over 5 years ago

Does anyone know how the continuous calibration of the altimeter works? How often does the recalibration take place?

On Sunday I was skiing between 1600-3200 m, yet when I reached a point which I knew to be 1800 m, the altimeter read 1950 m. I checked and saw that continuous calibration was enabled in the settings, but how does this feature work, and how often? When I manually calibrated using DEM, it changed straight to 1800m, so there was obviously no problem with the calibration process itself.

  • 0 over 5 years ago

    To me, how continuous calibration works, has always been a mystery...

  • 0 over 5 years ago in reply to renton82

    Haha yes, or it would seem it does not in fact, work.

    I checked the data again, at the beginning of the day it was reporting Alpe d'Huez village altitude as 1987 m. After calibration it was reporting 1804 (it's exactly 1804 m according to the official IGN maps).

    That's a pretty huge difference of 183 m (600' for the Americans)

  • 0 over 5 years ago in reply to simonjharris

    Same for me last year: started from Valtournenche (1524m), gone to Zermatt (1600m), come back to Valtournenche passing across Piccolo Cervino (3883m), and once stopped activity, altimeter on my Fenix 5 Plus reported 1750m! That's a huge difference! As i see here nothing changed with Fenix 6 series...

  • 0 over 5 years ago
    simonjharris said:
    checked and saw that continuous calibration was enabled in the settings, but how does this feature work, and how often?

    It's going to calibrate anytime  the barometer detects a change in pressure. In "auto", it goes between "altimeter" and "barometer" modes and does it's best to figure out it the pressure change was due to weather or actual elevation change. Sometimes it does this well, sometimes it doesn't. While skiing and your certain there will be little or no change in the weather, calibrate both the altimeter and the barometer to the correct readings. Then take the watch off "auto" and put it in "altimeter mode".  This way the watch will take any pressure changes detected as elevation changes only. 

  • 0 over 5 years ago in reply to tess

    Altimeter calibration mode and barometer mode setting are 2 different things

  • 0 over 5 years ago in reply to tess

    Figuring out whether it's due to weather or elevation changes should be easy by checking with the GPS altitude though. At the moment my fenix 6 is less accurate than my old FR235.

    Is it possible to turn off the barometric altimeter and just use GPS?

  • 0 over 5 years ago

    What I've found is that if you are hiking in an area with big altitude changes autocalibration does not work very well. I always deactivate this feature and my altitude is always pretty reasonable (normal changes due to pressure variation). If you imagine a case where you are in a very steep terrain and your GPS signal is not very good (let's say 15m error) the watch could interpret that you are 15m away from your true location and 200-300m higher / lower...

  • 0 over 5 years ago in reply to simonjharris
    simonjharris said:
    At the moment my fenix 6 is less accurate than my old FR235.

    This is because the 235 doesn't have a barometer and it uses geographical surveys.

  • 0 over 5 years ago in reply to renton82
    renton82 said:
    Altimeter calibration mode and barometer mode setting are 2 different things

    Yes, I know.

    Watch Mode

    Sets the sensor used in watch mode. The Auto option uses both the altimeter and barometer according to your movement. You can use the Altimeter option when your activity involves changes in altitude, or the Barometer option when your activity does not involve changes in altitude.

    Taking advantage of the fact that weather pressure changes occur at a slower rate than a person going up or down a hill, the unit will automatically transition between two modes; Altimeter or Barometer.

    • Altimeter mode locks the barometer value and assumes all pressure changes are due to elevation change
    • Barometer mode locks the altimeter value and assumes all pressure changes are due to weather
  • 0 over 5 years ago in reply to javier1892

    But GPS also provides an altitude, even if it's not super accurate it's never off by nearly 200m!