F7 pressure laboratory compare just for fun

trux said:

my test 1012.5 hPa), while the rawAmbient Pressure was 1014.15 hPa

Thanks for the info which explain everything! Don't You have typo in the text? Doesn't you mean 1012.5 vs. 1014.5? If You does, than the watch is right, but Garmin should show the temperature compensated value in default data field IMHO.

I'll try to find a possibility to turn the compensation off on the lab device.

The values are correct, but I do not completely exclude that I swapped the functions - I have the app on my watch since more than a year, when I wrote it, and I know I experimented with it, so it could have happened that the functions are swapped. I will have to re-check it later again.

... however based on your measurements, where your F7 shows ~2 hPa less than the lab device (if I understand it right), it seems to be the same case on my watch - it also shows ~2 hPa less on the barometer widget, than the hidden internal temperature-compensated raw value. So I think I have it indeed right.

Interesting, thanks for sharing!

honza_81 said:

Garmin should show the temperature compensated value in default data field IMHO.

Apparently it is not the case, as my test reveal. The widget uses the ambientPressure (uncompensated!) value, not the rawAmbientPressure (compensated). I know it sounds paradoxical, but it is indeed so. Finally Garmin tells it on several places that they use the noncompensated values. For example here: Elevation Accuracy of Outdoor and Fitness Devices | Garmin Customer Support

Since barometric altimeters are not temperature-compensated, changes in ambient air temperature can affect altimeter accuracy. If drastic changes in ambient temperature are experienced, calibrating the altimeter will restore accuracy.

Don't know which widget You mean. But on the watchface, the sea level pressure can only be shown and in activity, there is also the ambient pressure data field 

You are probably asking yourself (as I did too), what is the reason Garmin makes the extra job and removes the temperature compensation from the raw data of the sensor, just to get a non-compensated barometric data that then require frequent recalibration of the altimeter. On the first look it makes no sense at all.

However, if you think about it, you may perhaps understand the reasons behind it:

I do not know for sure, but my half-educated guess is that they do it because the pressure should be compensated to the air temperature, while the raw sensor data is compensated to the internal temperature of the watch, which can be often up to tens of degrees different than the ambient temperature. And since using weather data is unreliable, and indoors not applicable at all, they prefer removing the temperature compensation entirely.

In my case, I am at the sea level right now, so I use the barometer widget (same value as on the watch face - MSLP). I could also modify the CIQ app and plot both ambient and rawAmbient pressures and compare them directly, but as I wrote, since I am at the sea level, it is not really necessary. If I find some free time, I may do it later, anyway.

honza_81 said:

Thx, I'm going to install your app.

It is not available in the store, I use it only privately. However, I just reopened the source code of the app, and am checking it out. I will have to do some changes and re-run the tests. I am not sure I gave accurate information previously.