F5 - Barometer settings/modes/issues

It was good to find this topic. earlier today I decided to start polls about the ambient pressure accuracy of Fenix 3 and Fenix 3 HR. Here (https://forums.garmin.com/forum/on-the-trail/wrist-worn/fenix-3/1266116-ambient-pressure-not-barometer-pressure-accuracy-of-your-watch) and here (https://forums.garmin.com/forum/on-the-trail/wrist-worn/fenix-3-hr/1266121-ambient-pressure-not-barometer-pressure-accuracy-of-your-watch)

For those having F3 or F3 HR feel free to vote.

It is interesting to see that the barometer policy of Garmin has not changed (apart from the watch mode of altimeter/barometer/auto), so even for Fenix 5 family the ambient pressure measurement cannot be calibrated. If it is not perfectly accurate, an offset has to be used to get the true ambient pressure. And the same offset has to be applied for MSL pressure if one insists on the true elevation.

Not so with the Fenix 5 series, have a look at the software change log from 5.40 to 6.00 http://www8.garmin.com/support/download_details.jsp?id=11435

• Added support for manual calibration of the Barometer. (Settings > Sensors & Accessories > Barometer > Calibrate)
  

and I can confirm, on the Fenix 5 it does now allow you to do exactly what you wish to do with your Fenix 3 and 3HR but can’t.

Well we're still missing altitude setting from a known MSL pressure reading, maybe next time!

I’m not sure what the use case for that is. Anywhere you are likely to be given a known MSL pressure reading (weather station or similar) you are also going to have an accurate known elevation for that weather station. With those 2 pieces of info you first Calibrate the altitude on the Fenix 5 to that of the weather station you are at and then proceed to the next screen to enter the correct MSL pressure taken from the weather station. Your Fenix 5 is then correctly calibrated for both elevation and barometer readings.

Sorry, but I am confused. What does the new calibration method do?

If one can really calibrate the ambient pressure directly then indirectly the MSL pressure, since one can calibrate the elevation, too.

With reverse logics, if you know that your watch has a properly calibrated barometer (that is accurate ambient pressure) then you can easily compare the MSL pressure it shows and the official MSL pressure. With that you know what the accurate elevation you have to set.

OK, it requires some math, but finally you have an accurate barometer and altimeter. At least for one specific moment.

Sorry, I typed my answer pretty slowly because of watching a movie, but I am finally happy that somebody else has the same conclusion as I had.

Yes of course you can do the math (or use the "trial and error" method) but the reason all "real" ABC watches have that "altitude from MSL pressure" feature is so that you don't have to do it. Just get the METAR of your local airport (altitude not needed since it's MSL) and you can get your own altitude.

The new Fenix 5 barometer calibration allows you to take that correct MSL pressure for your location (I look mine up from the UK Met Office website) and enter it in to the watch; the watch has you do this just after entering the correct elevation for your current location. That then has your watch correctly aligned to the MSL pressure. The Fenix 3 and 5 have always displayed what should be the equivalent pressure at MSL in the barometer display, but folks had noticed that it was always offset by a few millibars from what that pressure should be as reported by meteorological sources. What the new calibration allows you to do is correct that offset. So if I understand what webvan would still like to see implemented, is that assuming you’ve got your Fenix 5 barometer calibrated as just described, the ability to later on (when the weather has changed) tell the watch what the correct MSL pressure should be at your location (from the meteriological source again) and then the watch should correct the altitude.

Yes that's what that feature does. I understand based on old posts that it was present on the original Fenix actually...but there was no calibration of the local pressure like what was added in v6.00 so the results were poor and people got annoyed ;-)

I just got the Fenix 5 two weeks ago and I LOVE it, but.... about this altimeter...

I recorded my last two outdoor cycling outings each with both the F5 and the Ride with GPS app on my Blackberry Passport. The F5 was, I believe both times, in Altimeter mode with Auto Cal on. The F5 is connected to my local ANT+ speed/cadence/hr sensors and the Blackberry is purely GPS and nothing else. Here are the widely varying elevation profile results:

https://ridewithgps.com/trips/19148164 - Ride with GPS?
https://ridewithgps.com/trips/19191247 - F5?

https://ridewithgps.com/trips/19231140? - Ride with GPS?
https://ridewithgps.com/trips/19246742 - F5

Now, before I return my watch or spend hours on the phone with tech support only to find out I have a faulty watch, I wonder if I just had it in the wrong mode. I did recalibrate the watch based on GPS, several times in fact, but I also notice that I lost 50ft of elevation today just sitting in the same place for hours after calibrating again.

I'm not splitting hairs over 10 feet but differences of 284ft and 431ft are bad. Then again, this is also dependent on how accurate RWG is too, but I would expect results that are a LOT closer to one another.

What mode should I be in and how should I be properly calibrating this thing for more accurate readings on my rides?