Garmin Mucks Up Altimetry - The5KRunner

Garmin Altimeters – “Way Off” Across The Board

Old Adage: “If it ain’t broke don’t fix it”

Garmin Exec: “Let’s fix it”

Thank you: Reader @Mike

A History of Altimetry

GPS gives you your 2D position on a map but it also can give you your 3D position and hence that third dimension is your elevation. That’s only as accurate as your GPS with the added complication of a longer time to get an initial 3D-fix than a 2D-fix.

Next, we have barometers that can accurately sense the number of times you climb the stairs each day from changes in air pressure over a few flights of steps. Similarly, they can be accurate when measuring your progress up the nearest mountain. Although that also relies on constant weather because changes in air pressure accompany changes in weather.

Anyway, if you put the two together (sensor fusion) you can get a pretty nifty level of accuracy which can be great when you are on that mountain or can simply be handy as bragging rights to confidently say how much you climbed each ride.

Satellite systems and other tech soon further improved matters as databases were created that assign an elevation to every GPS point on the globe with a Digital Elevation Model (DEM). Soon the likes of Garmin and Strava were post-processing your rides and giving you the option to get a super accurate post-ride elevation track.

More recently still, Garmin put the same elevation+GPS information into their watches and bike computers so that further data fusing of your position/altitude could be established.

And, you know what? It generally worked very well and so it has been for most of the last few years. There’s always some trickiness on steep mountain slopes and in cities but…generally…great.

Today’s Problems

But now it’s broken. Grrr.

Or at least a lot of people are finding it to be broken across generations of different devices. Grrr

• https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/instinct-solar/284275/the-terrible-altimeter-calibration-change-from-15-00-16-00-to-16-50-once-again-shows-everything-that-is-wrong-with-garmin-updated-same-problem-on-fenix-and-epix-2
• https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-6-series/282810/new-altimeter-algorithm-not-working-firmware-is-20-30
• https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-6-series/283340/we-need-a-third-altimeter-option
• https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-6-series/282735/altimeter-calibration-not-holding
• https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/epix-2/284181/altimeter-problem

Does Garmin Recognise This?

As an example, let’s take the firmware updates for the Fenix 6X (here).

I’ll just show the relevant bits to today’s discussion 🙂

Changes made from version 20.41 to 20.42 (Edit 5 Feb !!!!!!!!!!!!!) :

• Improved robustness to nightly altitude calibration.
• Fixed altitude calibration bug.

Changes made from version 20.30 to 20.41:

• Improved altitude calibration.

Changes made from version 20.20 to 20.30:

• Improved altitude calibration.

Changes made from version 19.20 to 20.30:

• Improved altitude calibration.

Changes made from version 20.03 to 20.04:

• Improved altitude calibration.

Changes made from version 20.01 to 20.03:

• Improved altitude calibration

Changes made from version 20.00 to 20.01:

• Improvements to altimeter algorithm

Changes made from version 19.78 to 20.00:

• Update the altimeter’s auto-calibration to be either be “On” or “Nightly”. Setting to “On” will calibrate at night, activity start, and continuously during activities. Setting to “Nightly” will set the device to only calibrate altitude at night.

Changes made from version 19.77 to 19.78:

• Improved altitude calibration.

Changes made from version 19.75 to 19.77:

• Fixed altitude calibration prompt before starting an activity. Prompts now only display on activities that use GPS.

I sense a pattern emerging!

So, as you can see, that’s a LOT of improvement to altitude calibration that’s going on. Or, perhaps more correctly, something got broken and Garmin is not quite sure how to fix it.

Me?

I don’t seem to be having these problems as this ride from yesterday shows with the Garmin Fenix 6 Pro, I’ll add some Fenix 7 / Epix Gen 2 data later on my experiences but they don’t negate what’s happening out there in the wild.

Interesting Afterthought

@Zoltan, in the comments below, found this gem of information about how Garmin’s algorithm establishes your starting elevation by relying on a fix from these prioritised sources:

1. Manual calibration immediately prior to starting the activity
2. Prior manual calibration point at the same location
3. Recent manual calibration, if the quality of the calibration is determined to be good enough
4. Map data (DEM), if available
5. Prior Connected DEM point at the same location:
   • Connected DEM refers to elevation data from the Garmin Connect app on a paired smartphone
6. Connected DEM, if currently connected to a phone
7. Prior GPS point at the same location
8. GPS, if a good fix has been acquired:
   • After acquiring a GPS fix the timer ring will turn yellow. At that point, it can take up to 30 seconds for the GPS elevation to settle. If vertical speed settles to less than .1 m/s the GPS elevation data will be considered good enough use for altimeter calibration.
   • Before starting the timer, the elevation data field on the watch will preview the calibrated elevation”

So it seems to be good practice to get a GPS fix outside your front door and then make a manual elevation calibration. Obviously, there is a handily named site for just that one purpose: https://whatismyelevation.com

Thoughts?

Your thoughts on how this has impacted you are welcomed below. I suppose the solace some of us can draw is that Garmin MUST be aware of this as they are continuously fixing it.

Hopefully, this doesn’t mark a return to the bad old days of releasing stuff that just hasn’t been tested by more than one person and their dog.

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Race Leader (tfk, the5krunner)

With 20 years of testing Garmin wearables and competing in triathlons at an international age-group level, I provide expert insights into fitness tech, helping athletes and casual users make informed choices.