I noticed that for the calibration of the Fenix 5 barometer two values must be introduced:
Current altitude ? crystal clear, manually or by means of GPS
Sea level pressure
The second item is not clear for me. If I'm not a sea level, which value must I introduce? The typical 1013.25 mbar? I noted that if I put any value in the sea level pressure the barometer is set to that value.
First of all. the Barometric Pressure shown on the watch is the same as equivalent air pressure at Mean Sea Level. This is the ambient pressure at your altitude, corrected to the air pressure you should expect to measure at your location right now, if you could take an elevator down to Mean Sea Level.
If you input a sea level pressure of 1013.25 millibar, the watch should show a Barometric Pressure of 1013.25 millibar. So it appears that your watch is functioning correctly in that regard.
Also, the air pressure at sea level varies all the time, approx. 30-40 millibar to each side of the standard value of 1013.25. So it would be very wrong to just input 1013.25 without knowing the real value for your location at the exact time you are doing the calibration.
So in short: If you don't know the correct value, don't input anything.
And I am inclined to say: Even if you know the correct value, don't input anything anyway if you have already input a known altitude. These two pieces of information are mutually redundant.
If you do want to input something, you should use the equivalent air pressure at Mean Sea Level, reported by a nearby weather station or airport. Airports have exact terms for this pressure (QNH). Weather stations are more sloppy, and it is not always easy to see whether they report true ambient pressure at their location or equivalent air pressure at Mean Sea Level. Most of the weather stations I have looked at will report the latter, though.
Disclaimer: I don't have an F5 and have not had a chance to experiment with this setting, so there may be something i have overlooked or ignored*. Others are welcome to chime in, but I have so far never seen any thorough discussion about this subject between F5 users.
*: There is a slight possibility that inputting both a known sea level air pressure and a known altitude will cause the watch to change its calculation of how much the air pressure should change for every meter your altitude changes. This could in theory make the altimeter more precise in cases where your altitude changes a lot. But there would be so many caveats in this approach that it would probably lead to increased errors more often than not. So I really don't hope that this is what the watch does.
Just been going through my watch calibrations after massive elevation spikes...
i too found this setting for sea level pressure and thought it odd to enter sealevel pressure if i was at 3000ft calibrating the altimeter...
just called garmin support and the support tech was unaware of this setting on his f5..so i talked him through to it and now he does know of the setting.
he said its probably to fine tune the calibration...although im still not sure why at a given set altitude you would enter the sea level pressure aswell...
so im going to experiment with estimated elevation pressure and known sea level from weather stations
It's there to correct the calibration of the absolute pressure reading on the barometer/altimeter unit.
If you have the elevation correctly set on the watch, the barometer should automatically show the value of QNH which Allan describes above, calculated from the elevation and the ambient pressure reading from the chip. If there's an offset on the calibration, then the barometer value will be offset, by the same amount no matter what your elevation or weather conditions. Entering your correct elevation and the correct QNH value lets the watch calculate and compensate for the offset, so setting the elevation correctly should always give the right barometer reading. You shouldn't need to do this often, it's not something that drifts quickly. I agree with Allan that you want to be pretty confident about the true value. Calling APIs for four weather services for the park round the corner from here currently gives 987, 988, 986.8 and 988, couple of weather forecasts say 986 and 987, most recent airport report is 988 but that's three hours old now.
The values are not mutually redundant, they combine to give an accurate value for the barometer for calibration.
Well since tuesday i calibrated my altimeter then went to barometer and entered as requested the current sea level pressure ...989mb based on uk bbc weather app...since then its been spot on ..ive checked randomly the pressure on the weather app and the f5 and its been with in 1 mb at worst but mainly spot on or .2 or .5 differance ..as we speak the weather app says 997mb for the current time my f5 baro has just changed from 996.6mb to 997mb...alto is 22ft lower than the known 225ft for my current elevation...this to me is spot on...
since tuesday i have gps tracked 80 miles of cycling and its been spot on....
so maybe the f5 baro sealevel pressure request in calibration give it a parameter to work from...which now i think about it differently it makes sense....as the option would not be there otherwise.
i realise ive probably just jinxed my device now but .. if all it takes is quick baro alt calibration with a very easy to find pressure even for a given time via the weather app ..maybe say once week id be very happy...
So if I'm not wrong, based on all your comments the best option would be just adjust the current altitude once in a while?
I correct the altitude at most once a day, if I'm somewhere I know what it is and I can see it's off.
I've corrected the barometer calibration twice, I think, the second time because I wasn't happy with the first one rather than because it had drifted. So, basically, do that once, keep an eye on the elevation and you'll probably be happy. Pretty much what BogWhoppitt says.
Hello. I have struggled to get my Enduro to record accurate Elevation Gains from my trail runs with lots of climbs. My reference is a trusted Fenix 3 HR that reports similar numbers as everyone who has done the same run with their Garmin, Coros, Polar GPS watches. A 35km course over 12 hours duration, my Enduro recorded 3000m-3,300m when on average, the others got between 2600-2800m. My Fenix 3 got 2688 ... reading your input here got me thinking how I could calibrate the Altimeter and Barometer for more accurate elevation gain.
The Enduro has no Altimeter 'Continuous Calibration' option and I discovered this when I did the 35km trail twice. The first time I had Barometer Watch Mode in 'Altimeter' it recorded 3,008m. The second time I had Baro Watch Mode in Auto and it shot up to 3,300m. It's ridiculous and I'm not getting anywhere.
