Altimeter creep

Same as the F3.
Reported about a hundred times and sadly it's still there.

And this could be solved by software: we ALL have POIs that could be used to autocalibrate the baro.

I was not aware this was a common issue.
I just upgraded from a F3HR which did not have the problem and I've sold it so can't compare again.
So what your saying is getting it exchanged for another F5X won't make a difference ?

Garmin support have told me to calibrate and let it sit in warm water for 15 mins.
Hasn't fixed it. Will see what they say next.

It doesn't sound like you have the alto/baro/temp issue that has beset some owners of F3 HRs (that issue has crazy large rapid swings in altitude). So it sounds like you've manually calibrated to 109m and then started a GPS activity (cycle, run or walk) and the altitude is not at the manually set altitude at the end of the activity. So the next thing to check is if your Altimeter Auto Calibrate setting (in the sensor settings menu) is On. If it's On then the watch recalibrates altitude to GPS altitude when you start an activity; so the error you see could be an incorrect GPS altitude calibration. If it's not already Off, it might be worth you doing a quick test with the Altimeter Auto Calibration set to Off.

I was not aware this was a common issue.
I just upgraded from a F3HR which did not have the problem and I've sold it so can't compare again.
So what your saying is getting it exchanged for another F5X won't make a difference ?

Garmin support have told me to calibrate and let it sit in warm water for 15 mins.
Hasn't fixed it. Will see what they say next.

Well... basically I calibrated to 150, gone down to the sea taking a straight road and correctly the baro marked 2... then back on the same road uphill and when I get there it's something like 156. All of this in about 20 minutes so it can't be a change in barometric pressure (and I did it something like 500 times).
It was there with the F3... it's not a "common issue" it's an issue that some didn't notice or pretended not to notice and it's apparently present in the F5x too (no exchanges done).
What's strange is that it always reads above the initial value when I come back to home location (150m) and never once below it... I have no idea why it did so with the F3 and why it does so with the F5x but I've only noticed it twice so far. Autocalib is off by default here: not a good idea in dense urban areas.

No matter how many times I manually adjust mine back to known altitude at my house, it's always up another 120' next time I look. F3 did the same.. useless

Well... basically I calibrated to 150, gone down to the sea taking a straight road and correctly the baro marked 2... then back on the same road uphill and when I get there it's something like 156. All of this in about 20 minutes so it can't be a change in barometric pressure (and I did it something like 500 times).
It was there with the F3... it's not a "common issue" it's an issue that some didn't notice or pretended not to notice and it's apparently present in the F5x too (no exchanges done).
What's strange is that it always reads above the initial value when I come back to home location (150m) and never once below it... I have no idea why it did so with the F3 and why it does so with the F5x but I've only noticed it twice so far. Autocalib is off by default here: not a good idea in dense urban areas.

Could be due to temperature. If you're wearing it on your wrist it might be warmer uphill due to exertion and that contributes to altitude.

Could be due to temperature. If you're wearing it on your wrist it might be warmer uphill due to exertion and that contributes to altitude.

Oh absolutely... but in 20' the temperature can't have changed much.
So when you drop from 150 to 2 you're ok and when you come back from 2 to 150 just 20' later you ready 156. It's like descent and climb are calculated differently (absent temperature changes).

If it's true (and it is true) that thermo affects baro, there should be an option to exclude thermo from the calculations for the elevation (i.e. unless I have tempe it's a completely useless instrument and if it affects the barometer it ALSO hurts an instrument that would work otherwise) ... but this would imply an ANSWER from Garmin that never came about this subject.

We don't even know if the elevation plotted by the F3/F5 takes ANY data at all from the thermometer.

Mine is the same

Mine stays at correct altitude until I use indoor workout and than it jumps another 120m. If I work out outside it stays correct. Auto correct switched off.

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Sometimes it works fine for hours

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Sometimes it drifts up 200' while keeping the overall accent/ decent correct enough and if the weather is bad enough it can also invert

The tempature change to the internal sensor when going from comfort to a true stable outdoor tempature is one of the bigger issues as when camping two weeks I have gotten the best performance

And this area often was more than my Ambit 3 could keep up with also

Oh absolutely... but in 20' the temperature can't have changed much.

This offset of 6 m at 150 m is around 4%.
Normally, you need 10 degrees temperature difference for this, which seems a bit high in this case.
Were you wearing the watch before or did you put it on and start? In this case it might be plausible.

Maybe next time wear it an a jacket pocket so that it doesn't get warmed by body heat or the sun. Just for this experiment's sake, I'm not suggesting you should wear it like that all the time :)
If the results are close, it might as well be the temperature.