Barometer elevation accuracy degradation over time.

My watch is still (1½ years after purchase) working well in this aspect. The elevation changes, that is measured by the barometer - and the input to that are some small holes on the watch. Have you tried soaking the watch in luke-warm water (non-salty!) for 20 minutes to see whether there might be something "stuck" in the hole affecting the elevation measurements?

https://forums.garmin.com/sports-fitness/healthandwellness/f/vivoactive-3-3-music/145228/clean-altimeter-holes

Hey oln65,

I'm relieved that you have a working device after 18 months!  I have tried washing it with warm water, but probably for a couple of minutes, rather than 20 as you suggest....I'll try it!

I just actually went through all my commuting cycles from work to home for 8 months, to check I wasn't crazy....this is what it read as (I clicked the "elevation correction" on and off for each one in turn.  Its about 23km / 16 miles (55 minutes) and the route barely varies by more than a street or two, so it does feel like something that's creeping up on me!

David

Same here. Replaced one 935 and two 945 because the elevation accuracy decreases over time. My problem was related to the temperature. Changes in temperature led to big changes in elevation. Over time it's getting worse and worse. Easy to check, put the watch in a cool place and see what's happening to the elevation. 

I gave up in the end and moved to a fenix. So far it's been spot on, fingers crossed: )

Have you tried doing calibration. Actually it is suggested to do calibration every time before you are doing an activity. You'll need the mean see level pressure to do it correctly or to know the current hight at the place you are (so that it can directly  map pressure to height). GPS hight is usually faaar from the real height and depending on the algorithms it could  result in additional wrong correction of the altitude. Even if your pressure sensor is faulty after a correct calibration it's should come out ok (as long as the faulting doesn't bring random changes to the pressure). Also usually pressure is highly dependant on the temperature and weather changes(the one if the reason for weather changes in the first place). So during expected temperature changes or weather changes it will come out with faulty readings for height(it may detect you a climbing for instance but the pressure changes because of the weather could lie to it and show you wrong data). This is the main reason airplanes has a special calibration knob(combined with special data string from the tower) and the modern receive the data directly from the tower for auto calibration (nearest mean sea level pressure).

Well....I never knew that about an airplane!

I definitely don’t calibrate before every exercise (life is waaaay too short), but my issue, a bit like an earlier commenter, is that it can start at the correct elevation, but is now getting more and more wayward during a ride.

I have recalibrated just in case, put my device in warm water for 20 minutes while standing on my head, and everything else Garmin suggests, however no improvement yet.

Apparently 20 data points are insufficient (according to support), for a meaningful comparison....I’ll keep trying all your suggestions though!

I rinse my watch and blow out the holes every day after every run so hope mine doesn't break too

Hi All,

I had the same twice with 935 and twice with 945. Exactly after approx. 6-7 months temperature and barometer sensor gone crazy and showed on my flat 10km track elevation gain about 200-250m where normally there is max. 15m. At the beginning (2-3 months) all devices show elevation gain correctly. But after this time it's growing and growing. All of them Garmin exchaged for me and I'm waiting when current will start to show strange numbers. Of course again I will report it to them for exchange.

The barometer port might be dirty.

I kept mine clean. Auto calibration at START of activity only.

The elevation is quite accurate for my 10 months old 945.

It is always clean ;)

What would the best settings be for auto-calibration? At the start/during activity - not during activity?