Altimeter performance test

Ich think your barometric sensor is broken. There are bugs causing flat lines, from that I am luckily not affected. But in your case it looks like random value of the sensor.

It is very different from one day to the next. The past night and whole day it was stable, and showing expected changes in altitude when I used the stairs at work. Until I went out for a run, then it started showing the random variations. All within +/- 20 meters, not hugely off. I have a hard time accepting my just new (3 months) old watch would have a broken sensor. But I'll keep an eye on it, if it gets to values over 1000 meters wrong I'm convinced it is broken.

I normaly get an repetitions accuracy of about 1%. Depending of duration of the activity because ambient pressure may also change. I also can resolve underpasses of streets going down 3m and then up again.

One thing which could happen to influence the altitude is strong wind. But Garmin has a very good filter here compared to the competitors. Saw this one in a mountaineering activity.

I apologize for my English. I've been having the same problem for some time now. I thought I was the only one who had this problem. At the start of each race, for about a month now, the altimeter makes a very exaggerated climb and then quickly descends, distorting the positive meters in my trail races. On the other hand, the floors climbed are always 30 or 40 even when I don't climb floors all day. The barometer suffers exaggerated variations; the altimeter suddenly climbs many meters and then immediately descends. Could my barometer be broken? It could be, yes. But I see that I'm not the only one who has this problem.

There are a lot of threads here in the forum about strange altimeter readings. Also some indication that pool swimmig with treated water (chlorine) wears the barometric sensor out pretty fast.

I'm lucky and my readings are fine since 2 years. Always max 1% deviation between ascend and descent when running and mountaineering and all the readings are also compareable with the watches of my friends from other brands.

So I'm satisfied so far. So if you are not satisfied I would directly write the customer support for repair under warranty and collect evidence that there is a systematic issue with the device.

I am having similar issues with my watch and posted a thread about floors climbed a month or so ago. I think it is a software issue, maybe if we make enough threads they will look into the software side of the watch to double check it isn't a bug?

Can be that there are wrong calculations unter certain circumstances. I have never encountered any with the altitude since two years now.

But referring to the screenshots of Data is was either pretty windy and the oder screenshots of Fenix are from other days or his barometric sensor is broken.

The 3 screenshots at fhe top were of the same timeframe (taken a few seconds apart) and of the same activity.

I posted a theory in this thread: https://forums.garmin.com/sports-fitness/running-multisport/f/forerunner-955-series/396583/still-experiencing-elevation-inaccuracy-on-the-955-fridge-experiment-and-more-example-runs

I think the algorithm in the Fenix 5 and 6 is tuned a little differently.

Another day, another test, and completely differemt results. All three watches showing the same erratic drift. I will update my first post.

Can you tell us more about your setup?

Do you wear all watches at the same time and where do you wear them?

Here are some examples from my activities wearing the watch always on the left wrist on different activities crossing the same endpoint.

Coast run

Seems pretty flat 3m difference between starting and end. Some change might also be due to having not exactly the same ending point.

Via ferrata

You can see a drift here at the summit of about 10m which I end about higher than starting.

Very windy day especially in the wall you can see at the wiggling graph on the ascend.

Mountaineering

Ending point (red circle) also pretty close to starting. There is only a slight difference od a few meters.

Trail run

Starting end ending point at the same height (1m difference)

So in my case I can say the altimeter works better than I ever expected and deviations, if there, are small and reasonable.

I had around 250 activities this year and never encountered something suspicuious so far. So either I have an espically good device or yours is broken or some other circumtstances are influencing your results.