Temperature change causing elevation during activity

When the watch is in 'barometer' mode, it should keep the altitude constant and interpret all pressure changes as weather changes (the sea level corrected pressure will change)

If you're doing activities in barometer mode, then you're using the wrong mode, and that should be your first thing to change.

In auto mode the software guesses as to whether the pressure change is due to weather, or actual elevation change.  Sometimes its right, other times its wrong, so use 'altimeter' mode to keep it from guessing.

the accuracy/dependability of auto calibration mode has been questioned here by others, I never use it so I have no opinion, but it would be worth experimenting with that being off or on to see if that makes any difference.

As far as temperature affecting the altitude reading, I took mine from about 80F to 40F by putting it in my refrigerator, and the altitude only varied by a few feet (<10).  I did the experiment on three digital altimeters at the same time, they all had similar response with temperature.  It looks like your watch only experienced a 10-15C temp change, so less than the change in my experiment, so yours should have been within 1-2m based on temperature change.  Since the change was so small and I pretty much ignored it, I can't recall if the altitude went up or down based on the temperature getting colder.

Thanks for your extensive reply. Browsing through my first few activities from a year ago, i see a much smaller (or even neglibile) effecr of temperature on elevation. So either HW or SW was fine...

Regarding the watch mode: if running mainly on flat terrain (Netherlands), why would 'barometer' be wrong?

DaanvS said:

Regarding the watch mode: if running mainly on flat terrain (Netherlands), why would 'barometer' be wrong?

Barometer mode is intended for use when you are indoors and it makes the watch behave as if it were a barometer hanging on the wall.  It knows the altitude isn't changing, so the altitude stays locked at whatever value it was at when you entered barometer mode.  I don't see what purpose that would serve during a run, since your altitude would be reported as a flat line over the entire run. 

You could also argue that seeing the altitude fluctuate by a few meters like in your latest graph doesn't provide much information either, but at least that graph is representative of what really occurred during the run.

Its frustrating that it used to work properly and now it doesn't, firmware changes seem to often have unintended consequences with this watch.  I turned off the auto update and have my firmware at 9.0 because once I had it working the way I liked I didn't want to be a victim of newer updates causing problems on things I cared about, while fixing things that I didn't care about. 

Garmin should allow users to download and install any version of firmware they please, because it seems like their updates often cause new problems based on things I read here.  Not being able to go back to a previous version that worked better is a dis-service to their customers.

5693709 said:

Garmin should allow users to download and install any version of firmware they please

The downside of allowing people to work on different FW versions is tech support won't know how to assist you.  I have this issue, on this watch FW, using this version of GCM and this version of Garmin Express.  What a nightmare that would be.   I imagine you'd also have issues with some ciq apps also.

5693709 said:

Not being able to go back to a previous version that worked better is a dis-service to their customers.

I'll have to disagree here.  I believe having users and support on the same sheet of music is more beneficial to the customer.

I'll have to disagree here.  I believe having users and support on the same sheet of music is more beneficial to the customer.

Normally I'd be in complete agreement with you, but in this case I've seen the quality level of Garmin's firmware updates and they don't impress me, which is why I don't use them.  If they didn't break things on every new release it would be a different story, but this forum is full of "it used to work before a firmware update" stories.

5693709 said:

If they didn't break things on every new release it would be a different story, but this forum is full of "it used to work before a firmware update" stories.

I hear this said over and over.  It's an exaggeration. I've been with Garmin for almost a decade now using several different watches and I've seen maybe 3 instances where an update messed something up out of maybe a 100 I've gone through over the years.  I'm not saying it doesn't happen.  I'm saying with all the different configurations, set-ups, phone make and models, I expect there will be some with difficulties on every FW release.  For the record, my barometric altimeter is working fine.  Anyone who says every update breaks something new on their watch isn't being honest, though I'm sure there will be a few who are ready to reply with this was the case for them.

If you want accurate altitude readings.

Put barometer into altimeter mode

disable auto mode

disable calibration before activity

disable calibration during activity

Before activity manually calibrate altimeter to a known height, say a trig point or contour line or you just know the altitude

Now any changes in pressure will be considered to be changes in height, +/- about 10 feet or so.

Caveats

If your activity is short then the altitude recorded will probably be pretty accurate

If during your activity the weather changes such that the pressure changes, this will be recorded as an altitude change. So this would include:

        Air temp change affect pressure

        Relative humidity affects pressure

        Even local gravitational changes affects pressure (unlikely to notice this one)

To counteract this recalibrate altimeter often. In GA aircraft a pilot may recalibrate the barometric altimeter every 10 - 30 mins or whenever they know the pressure has changed by talking to ATC.

I use my F6X in this way and the altimeter is pretty accurate.

I hear this said over and over.  It's an exaggeration.

For the record, my barometric altimeter is working fine. 

Mine too, works perfectly every time I use it, but I see a lot of other people having issues with altitude readings.  Some problems may be due to user inexperience, I dunno, but others, like the random spikes in elevation over a run just have me shaking my head, that's not a user issue.

I assumed that with watch mode in 'barometer', the elevation during an activity is based on GPS + DEM instead of GPS + DEM + barometer. Since the temperature to elevation impact is likely coming from the barometer (directly or indirectly), i thought watch mode on 'barometer' would be the most logical thing. 

regarding the SW I have mixed feelings. SW development is becoming more and more complex as it is hard to keep up with all the baselines over the various products while implementing all kind of new features. I recognize that some features break / change as a result. Boeing is not the only company struggling with SW If SW updates are done properly (ie clean improvements without breaken/changing other features), being all on the same FW is highly beneficial for everyone. 

2572376 said:

If during your activity the weather changes such that the pressure changes, this will be recorded as an altitude change. So this would include:

        Air temp change affect pressure

        Relative humidity affects pressure

        Even local gravitational changes affects pressure (unlikely to notice this one)

I fully agree; though +30m for a 15C drop is a bit too much (see case A above) and suggest a HW or SW failure. Agree?