Related

Barometer and altimeter mismatch

byf3332
5 months ago

I took an airplane ride yesterday, and it's obvious that the air pressure will drop a bit as the plane rises. But my watch tells me the pressure *rises*, but strangely the altitude also rises, which shouldn't be the correct behavior. Also when the plane descends, the pressure is still rising?? From the picture you can see 2 rises of air pressure.

Any solutions? This is really strange.

  • 0 5 months ago

    HI, I'm not an aviator but I do hiking and mountaineering. After 2 years of using the fr955 I have to tell you that the altimeter and barometer functions are rather poor and have disappointed me. when I go up to altitude and obviously the atmospheric pressure drops, the Garmin warns me of storm risks. when I calibrate the altimeter by entering an altitude, the barometer consequently changes value and the graph. the atmospheric trend arrow in the ABC widget has always been in the horizontal position for 2 years. The altitude measurement is often off by several meters, I tell my friends with other devices here when we go to the mountains... in short, if it weren't for electronic payments I think I'd switch to Suunto. Bye.

  • 0 5 months ago
    byf3332 said:
    From the picture you can see 2 rises of air pressure.

    Ahem, you are not looking at the same timeslot, obviously.
    The first is 16-19, the second is 2-5 - obviously being completely different hours of the day.

    Albertone said:
    the altimeter and barometer functions are rather poor and have disappointed me

    Personally I think, the „auto detection“ of if a pressure change comes from moving or from weather is not very good, so it might help to set that to manual when going to the mountains (when it is important…).

    Other than that, I had good experiences. For example drove hundreds of kilometers by car and changed by hundreds of meters, and at the finish (without calibrating, or starting a GPS based activity that might auto-calibration) the altitude was correct within 10 meters.
    I expect no more.

    Also for activities usually it is alright for me, but definitely not perfect.
    I think the problem is, there are quite some watches with altitude hardware failure in the wild.

  • 0 5 months ago in reply to Grumpy from dawn till dusk

    im quite sure the graphs are at the same time, idk why the time didn't match at the bottom, but  you can see that i manually set the little white dot to both at 18:30 Mon.

    Altimeter works fine, but barometer seems to be incorrect, unless i set sensor mode to barometer only.

  • +1 5 months ago

    There's nothing wrong with your device. The barometer plot doesn't show actual (ambient) pressure. It shows sea-level pressure, i.e. what the pressure would be at sea-level given your current elevation and the ambient pressure measured by the device.

    Cabin air pressure in commercial aircraft is typically equivalent to about 1600 to 1800 m elevation. That's consistent with your altimeter plot.

    The reason why the charts show variations in both elevation and sea-level pressure is because you've got auto-detection enabled. With this setting, the device assumes that a rapid change in ambient pressure is due to a change in elevation, not a change in sea-level pressure. However, if the change in ambient pressure is more gradual, then the device assumes that your elevation is constant and sea-level pressure is changing. It looks like your device was switching back and forth between the two modes. At first there was a rapid decrease in cabin air pressure, which your device registered as a change in elevation. But then there were further minor variations in cabin air pressure, which your device interpreted as a changes in sea-level air pressure.