I got some issues with the altimeter readings on my series 6 44mm gps. It was correct at first (~20m elevation) and in line with my iPhone's compass readings. Then it suddenly started reading out ~200-250m, even when I was at sea level. I tries restarting and unpairing/pairing the watch, and the latter seemed to have fixed it, but now it's showing like ~2-3m, when it should be ~20m. Apple's claiming 2ft accuracy on this if I remember correctly. I don't really use this feature, but have noticed the wildly different min/max elevation in my recorder workouts. Also, if I restart the watch, there's no elevation reading for a while and I have to start a workout and end it to force it to show. Anyone else experiencing similar issues?
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Series 6 altimeter issues
- Thread starter hyperfeel
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Generally speaking, barometric altimeters are best at relative elevation changes rather than absolute elevation. I am unaware of Apple's claims of accuracy; if you could point to where that's published I'd appreciate it.
Anecdotally though -- Looking at the data from my little rooftop weather station, I've seen barometric pressure change by 0.44inHg in the past couple days. That'd represent about a 400ft elevation difference -- simply due to weather changes.
This is why most barometric altimeters need to be calibrated against either a known elevation or against a known barometric pressure reading (usually adjusted for known elevation of the weather station - see difference between Relative & Absolute Pressure), and then recalibrated again when possible.
I'm unsure what mechanism the Apple Watch uses -- perhaps GPS -- which has it's own issues with elevation accuracy, with +/- tens of meters elevation very typical even as a best case.
See:
eos-gnss.com
and:
Anecdotally though -- Looking at the data from my little rooftop weather station, I've seen barometric pressure change by 0.44inHg in the past couple days. That'd represent about a 400ft elevation difference -- simply due to weather changes.
This is why most barometric altimeters need to be calibrated against either a known elevation or against a known barometric pressure reading (usually adjusted for known elevation of the weather station - see difference between Relative & Absolute Pressure), and then recalibrated again when possible.
I'm unsure what mechanism the Apple Watch uses -- perhaps GPS -- which has it's own issues with elevation accuracy, with +/- tens of meters elevation very typical even as a best case.
See:
Elevation for Beginners: What to Know About GPS Receiver Elevation | Eos
What is the difference between the ellipsoid, mean sea level, geoid, geoid height, and orthometric height? Here's everything to know.
eos-gnss.com
and:
Last edited:
Thanks a lot for the thorough explanation. Relative readings do seem to be consistent, so I guess that's good. With regards to the accuracy claims, I think I heard it in a review video somewhere but it might have referring to the elevation gain accuracy rather than the absolute elevation. I genuinely thought this was an actual hardware issue with the watch and considered contacting Apple for an exchange.
Happy to help.
When I first started digging into this, I was a bit surprised at how much the natural weather based changes in air pressure could affect a barometric altimeter. I'd always heard one needed to adjust/calibrate frequently due to weather but just haven't looked to see how much different it really could make over a matter of days.
When I first started digging into this, I was a bit surprised at how much the natural weather based changes in air pressure could affect a barometric altimeter. I'd always heard one needed to adjust/calibrate frequently due to weather but just haven't looked to see how much different it really could make over a matter of days.
the absolute value accuracy they claim is variable and can be seen in the compass app, it's the gain they claim to be accurate.
Right now mine is displaying +-50m absolute accuracy, though it is actually within 5m.
Right now mine is displaying +-50m absolute accuracy, though it is actually within 5m.
I can't say I have been too pleased with the "always-on" altimeter, especially during an activity...
https://strava.app.link/URJsbjSrrab
A perfectly flat area- elevation gain of 6m
https://strava.app.link/YG4Lw6Yrrab
Another mostly flat area- elevation gain of 13m
https://strava.app.link/URJsbjSrrab
A perfectly flat area- elevation gain of 6m
https://strava.app.link/YG4Lw6Yrrab
Another mostly flat area- elevation gain of 13m
