How to set the barometer as a weather indicator tool?

I set the altimeter manually to the known local altitude (337 meters in my case). I switched off the altimeter autocalibration based on GPS. I set the same altitude in the barometer settings, then I set the sea level pressure at 760 mmHg (as this is the well known standard, right?), and I finally set the Watch Mode to barometer. Now the altitude is frozen at 337, even when I descend 3 floors from my apartment (at least 9-10 meters equivalent) to the ground. The only parameter which is changing is the barometer pressure, it changes slightly from 760 mmHg to 760.7 or so, when I descend from the third floor to the ground. When I'm at the third floor, staying inside my apartment, the barometer is almost frozen most of the time (ranging between 759.8 and 760.1). I must mention that the real time pressure in my city is now around 735 mmHg and rising, as the local weather station shows. I'd like to see the barometer changing according to weather changes, so how should I set the altimeter/barometer in order to achieve that? Or is my watch a lemon? The sensors/software are broken? I need your advice. Thanks.

Later edit: I just discovered an Ambient Pressure widget, which shows 733.4 mmHg, very close to the real pressure measured by the local weather station, which is 735 mmHg, as I already said. OK, so, what is the difference between "barometric pressure" and this "ambient pressure"? Is one influenced by the other? Can someone explain? One more thing, in this widget, under the 733.4 mmHg pressure is displayed the altitude (which is 337 meters, as I said), and another pressure indicator (I suppose), which shows: 766.4. So what does this represent?

0 al_pacino over 6 years ago

It seems it's a software error, which appears only when you open the GPS connection through an activity tracking. I was on the same route last night, but didn't activate the GPS, and when I got home I saw the correct altitude, so the altimeter hasn't drifted like last time. So, I presume it's a software bug, which changes altitude when GPS is activated, even if the watch mode is set up for barometer and altimeter autocalibration is also off.

0 AllanOlesen67 over 6 years ago

I can't help with that one. I have never used my Fenix 3 in forced barometric mode, and I don't even think it has that setting. But as you, I would expect the watch to never change its altitude in forced barometric mode.

0 al_pacino over 6 years ago

Maybe I should set the altitude autocalibration ON, maybe this is the case it's intended for.

0 AllanOlesen67 over 6 years ago

I can help with some tips on GPS autocalibration of the altimeter.

First, it is important to know that the watch keeps track of known altitudes:
The watch keeps a table of known location/altitude pairs. An entry is added to this table every time you manually calibrate the altitude while the GPS has a fix.

When you start an activity while the GPS has a fix, the watch will look up your current GPS location in the table and use the known altitude from that table. If there is no known altitude recorded for your current GPS location, the watch will use the current GPS altitude.

So to get the best out of GPS autocalibration of the altimeter, try to follow the recommendations below:

Setting up the watch (only necessary once):

Find the correct altitudes for all locations where you will usually start an activity. Use a topographic map or whatever info you have. Or average the GPS altitude readings over a very long time.
Make sure that all these start locations are in flat land so you always start the activity at the same altitude.
For each of those locations: Go to the location. Start an activity so the GPS is running and has a fix. Go into the ABC widget while the activity runs in the background and set the known altitude.

Starting an activity (necessary every time):

Make sure that you are close to one of the locations recorded in the altitude table. (Within 25 meter will usually do the trick.)
Go into the activity app and wait for the GPS to get a fix.
Press Start.

If you want to watch what the watch is doing during the steps described above, it can be very helpful to have a custom data screen showing both Elevation and GPS Elevation and looking at this screen while starting the activity. Try this:

Stand at a location 100 meter away from a known location in the altitude table.
Go into an activity app and browse to the custom data screen with the two Elevation fields.
While you have no GPS fix, you will see the Elevation field showing whatever altitude the watch thinks it is at right now with its current altimeter calibration. The GPS Elevation will show nothing.
When you get a GPS fix, the GPS Elevation will show an elevations which goes quite a bit up and down (GPS altitudes are noisy). And the Elevation field will mimic the GPS Elevation (well, sometimes it doesn't, especially if you very recently did a manual altimeter calibration at another location).
Start moving towards the location recorded in the altitude table.
When you get near to this location, you will see the Elevation field jump to the recorded altitude from the table and stay there, no matter how much the GPS Elevation field goes up and down.

If you at any stage during these 6 steps press Start in the activity, the altimeter will be recalibrated to the current reading of the Elevation field. What then happens during the activity seems to depend somewhat on firmware version. Some versions will use this calibration throughout the entire activity even if they get better altitude information during the activity. (Which to me is desirable because I am more interested in altitude variations than in absolute altitude.) The latest version for the Fenix 3 may be different - I have seen it do a sudden altitude jump shortly after starting an activity, probably because I started the activity before the GPS discovered that I was at a location from the altitude table.

If you leave the activity app without pressing Start, the altimeter will just continue using the calibration it had before you entered the activity app.

This is the behaviour of a Fenix 3. From what I have read in other threads, I think you should see the same behaviour with the Fenix 5.

0 oleksiy.yergiyev over 6 years ago

Thanks for the insight. I've tried this on my VAHR, only I used altitude calibration in the sensor menu since I don't have an ABC widget. The result is quite surprising - the feature works but in an unexpected way. Apparently, it links barometric pressure to location rather than altitude. In my case, I calibrated the altitude to the real 176 m near my office the day before yesterday, and then both yesterday and today the watch re-calibrated itself from 190 and 196 m to 228 and 227 m immediately as I approached the place. Readings from the Ambient pressure widget today:

Before the "location" calibration
ambient pressure 745.3 mm
altitude 193.6 m
barometric pressure 765.2 mm

After
ambient pressure 745.1 mm
altitude 227.4 m
barometric pressure 767.7 mm

Will monitor further if that's the barometric pressure that gets sticky, or if it's just an offset from the manually calibrated 176 to 227-228 m.

0 AllanOlesen67 over 6 years ago

I am not sure I understand. Have you seen it autocalibrate to the same barometric pressure twice, but to two different altitudes? This would be a clear mistake.

However, it is not a mistake that it changes the barometric pressure when you calibrate the altitude. The barometric pressure is calculated from the ambient pressure and the altitude, so a new altitude will give a new barometric pressure. (But I think you already know this. I recall seeing that you explained this quite eloquently in another thread.)

0 oleksiy.yergiyev over 6 years ago

Sorry for messing up with the explanation. I was trying to say, that the altitude lock and consequent calibration didn't work properly in my case. Having calibrated it to 176 m according to your instructions, I had the altitude on my VAHR jumping straight to 228 m as I approached the "altitude lock" location near my office the following day. Hence, I thought that there could be two ways to explain this. The first one, my VAHR put some other arbitrary altitude into its "table" of known altitudes / locations - 228 m instead of 176 m I input manually in this case. Or, alternatively, VAHR somehow locked barometric pressure that was calculated from the ambient pressure and 176 m altitude at the time of calibration, and wrote it up in the "table" instead of altitude, and then inserted this very barometric pressure value the next day when I verified if the set up worked. Since the ambient pressure may have changed, the watch recalculated the altitude to match this "locked" barometric pressure accordingly.

I.e., having ambient pressure as a input from the watch sensor, you could either calculate altitude if you know the true barometric pressure, or arrive to the barometric pressure value if you know the correct altitude. So I just thought that any option is possible, that's why I wanted to check things further. Hope this makes sense.

Now, after today observation, I believe my second hypothesis should be true. Something messed up with the altitude calibration, and although I input 176 m, the watch recorded 228 m instead. I'll check whether this is a one off error, or it's a permanent 52 m offset and I should calibrate to 124 m instead for this location.

I had these values today:

Prior to approaching the location of auto-calibration to the recorded 176 m altitude:
ambient pressure 742.4 mm
altitude 182.8 m
barometric pressure 760.8 mm

At the location of auto-calibration to the recorded 176 m altitude:
ambient pressure 742.3 mm (745.1 mm yesterday)
altitude 227.2 m (227.4 m yesterday)
barometric pressure 764.8 mm (767.7 mm yesterday)

0 lk130 over 6 years ago

Slightly off-topic, but where can I see Ambient Pressure on the 5S? I know only about Barometric Pressure. Or does it require a non-stock widget?

0 AllanOlesen67 over 6 years ago

Slightly off-topic, but where can I see Ambient Pressure on the 5S? I know only about Barometric Pressure. Or does it require a non-stock widget?

There are two widgets which can show ambient pressure:
https://apps.garmin.com/en-UK/apps/00678298-6672-4228-9c82-c9aa00e43df0
https://apps.garmin.com/en-UK/apps/1e896cb8-87ac-4b7a-869f-b1c053fd917d

Ambient pressure is also a native data field which you can use in any data screen within an activity. This can be set up directly in the watch.

0 AllanOlesen67 over 6 years ago

Now, after today observation, I believe my second hypothesis should be true. Something messed up with the altitude calibration, and although I input 176 m, the watch recorded 228 m instead. I'll check whether this is a one off error, or it's a permanent 52 m offset and I should calibrate to 124 m instead for this location.

Is it possible that you have earlier made another manual calibration nearby, and the watch is locking on to this old calibration instead?

As far as I know, we have no option of viewing or editing the table of known altitude/coordinate pairs, and that makes troubleshooting in such cases more complicated.