Series 6 Altimeter Discrepancies

[StumpyBloke]

I’ve noticed today, possibly since the 7.0.1 update that the stock altimeter app shows a substantially different height to the My Altitude app. I know that the My Altitude app is correct because I’ve looked on Google Maps and it is exactly right for my location. There is about 10-15m difference between the two which is ridiculous. Could anyone confirm theirs are accurate please? Thanks.

 

[jdb8167]

Interesting. The elevation of my house seems to have dropped 15 ft.

 

[michaelb5000]

I haven't noticed anything this week, but I haven't had the S6 long enough to really test the altimeter (it seems to work great). But I think the key here is that altimeters don't have any way to know your initial position. Altimeters are used to measure your change in elevation over time, so as you move. I am pretty sure you getting your initial position from GPS, possibly aided by cellular or wifi. All of those methods are notoriously error prone in terms of elevation (much more so than GPS location). So having your initial position bounce around on an altimeter is normal. Many altimeter/barometer apps let you set your initial position. Did you do that or ever do that for "my altitude"?

 

[Böhme417]

My Altitude reads lower for me using the device sensor than it does when using gps data.
~10 m difference

 

[wilberforce]

Barometric altimeters have high relative accuracy, but low absolute accuracy, as the ground-level barometric pressure varies with the weather. Hence they need to recalibrate to ground-level altitude determined by other means such as GPS, or the known elevation of your location (from map data), or, in the case of aircraft, the airport's precisely measured true barometric pressure at ground level.

 

[deeddawg]

GPS elevation is notoriously inaccurate. Has to do with the way the location is calculated. 2-dimensional accuracy can be good, but z-axis is usually not so good. https://www.geoawesomeness.com/accurate-altimeter-gps-watch/

I'm unfamiliar with My Altitude. Does it account for current barometric pressure at your location?

 

[StumpyBloke]

Interesting. The elevation of my house seems to have dropped 15 ft.

Is that since updating to watchOS 7.0.1? I am reasonably confident that before this update, the figure was virtually identical to the MyAltitude one.

I recommend the MyAltitude app, and it’s free. Would be interesting to see if you get the same discrepancy.

 

[StumpyBloke]

Thanks for all the replies. I’ve added two pictures from the MyAltitude app which hopefully will answer your questions, this is all above my head. One shows readings from the sensor and the other shows readings from its data files. I don’t think there is a fault with the altimeter because the MyAltitude app shows the same figure as on my previous series 5 watch.

Meanwhile, my watch using the stock altimeter app shows 70m currently.

Edit: and I’ve just checked again two minutes later and it’s now showing the correct reading of 86 m. Really don’t understand this. It’s been wrong for hours and hours and hours and now it’s suddenly correct.

 

[StumpyBloke]

To add, it’s now showing the elevation as 86m followed by plus or -5 m. When it was showing the elevation of about 70 m it said plus or -10 m.

Whilst staring at it it’s still showing 86 m but it’s now changed to plus or -10 m. I wonder where it gets the location from?

Edit: apparently it’s a barometric altimeter

 

[deeddawg]

@StumpyBloke I'm going to venture a guess that location comes from GPS. The +/- 23.91m is a pretty typical margin of error for non-ideal conditions.

As for 70m +/- 10m and 86m +/- 5m -- are you in a flat location or does the ground topography change somewhat? Reason I ask is that from where I'm sitting right now, 20m one way vs the other would definitely account for ~5m elevation differences.

Also note that air pressure changes a bit under 1mmHg per 10 meter elevation change (when near sea level). The two photos show a difference of over 3mmHg, and thus just that would represent a bit over 30m elevation differential (unless I'm way off in my math?)

I think the takeaway here is I don't think we can expect substantial accuracy or agreement on absolute elevation information, particularly when the underlying data sources are unknow. Are they working purely from barometric pressure? Is the know pressure at a known location that day factored in? Is the ground location being used in some way, and if so what specific metric is being considered? Is GPS elevation being considered, which is already known to have a high level of variance from actual?

Finally - what's up with displaying Pa, kPa, and hPa on the same display? Can folks not move a decimal point quickly in their heads?

Edit - checked my AmbientWeather weatherstation. Since 24 hours ago, relative pressure here has gone from 765.556mmHg to 760.222mmHg -- and at ~14mmHg per 150m (appropriate for my elevation), that'd show a 40+ meter elevation difference?

Kinda out of my usual territory here so please correct my #'s if I've botched something. General point is barometric pressure is good for relative differences in elevation but gets complicated to use it for absolute elevation.

https://www.avs.org/AVS/files/c7/c7edaedb-95b2-438f-adfb-36de54f87b9e.pdf

Atmospheric Pressure vs. Elevation above Sea Level

Elevation above sea level - in feet and meter - with barometric and atmospheric pressure - <i>inches mercury, psia, kg/cm² and kPa</i>.

www.engineeringtoolbox.com

 

[StumpyBloke]

Thanks again for your reply. I really don’t understand the technicalities. I guess I was expecting the figures to be the same across different applications whether stock or not because it’s taking readings from the built-in sensor. The stock app has now dropped to 81 m plus or -5 m and MyAltitude app shows 85.9 m plus or -10 m. Oh well...

 

[ApfelKuchen]

The Device Sensor barometric reading is different than the Data Files reading. That alone can account for the difference in calculated altitude. While GPS data can also be used, the accuracy of GPS on a watch is such (typically +/- 30-40 feet) that it may not tell the whole story - anyone who has hiked in hilly terrain would appreciate that. A combination of GPS and barometric pressure is potentially more accurate.

Presumably, Data Files is coming from a local weather station. One would hope the weather station's sensors are more accurate than the Watch's. However, conditions at the weather station may be different than at your current location (altitude, location of weather front, etc.).

Altogether, you have to take all of this with a grain of salt. For the Data Files-derived altitude, it shows an accuracy of +/- 3.00 meters. For the Device Sensor-derived altitude, accuracy is +/- 8.01 meters. That is almost definitely attributable to the expected accuracy of the Watch vs. the weather station instruments. In the end, it is what it is. Compare a $400 Watch with a long list of components besides the altimeter to a weather station instrument that undoubtedly cost thousands of dollars... you know which should come out the winner.

I'm a hiker and live/hike in a hilly area - it's nice to have altitude data from my hikes, but I can also access far more accurate elevation data from mapping resources. If I reach the top of a hill, I don't need an altimeter to know how high I've climbed. I find it fun, however, to get a total elevation number from my Watch that accounts, more or less, for all the little ups and downs along the trail. Overall accuracy isn't important, as I'm not a map-maker - it's just a fun statistic that doesn't really need to be spot-on accurate.

 

[StumpyBloke]

Another thing I’ve noticed is when I tilt my wrist(watch) from level 0 degrees incline towards me it goes to 54 degrees then to 0 degrees. What’s that all about?

 

[deeddawg]

Another thing I’ve noticed is when I tilt my wrist(watch) from level 0 degrees incline towards me it goes to 54 degrees then to 0 degrees. What’s that all about?

Switching from horizontal reference to vertical reference.

 

[StumpyBloke]

Thanks. When it is showing 54 is more likely about 80. Really don’t see the point of it on the watch.

 

[StumpyBloke]

Just revisiting this. I went on a reasonably short walk today of about 1.5 miles on quite flat ground. The readings on the series 6 altimeter ranged from 87 m (correct) and then a few metres down the line 150 m and back again. Now bearing in mind this is flat ground these readings are nonsensical and an absolute waste of time. The weather was overcast and damp but not raining and about 10°C.

I genuinely can’t work out how this is meant to be of any use. Does anyone else get such ridiculous readings? I’m in the UK by the way.

 

[McKain]

I found the GPS on the watch while hiking in the Scottish mountains extremely accurate, + or - 5m accuracy compared to OS map data.

While testing the watch I put it into airplane mode (GPS still works) and over the next few days I walked to the same point on a small hill and the altitude readings were virtually identical. Atmospheric pressure was different each day so the watch does not use the built in barometer for readings.
Remember for accurate GPS readings you have to be outside with a clear view of the sky, also make sure you are not connected to your phone as I have a feeling the watch uses the phones GPS sensor to save battery.

As for for the tilt part, I’m guessing its for taking a reading from the built in compass, making sure sure the watch is as flat as possible before taking a bearing.

All my tests were on an AW 5 with watch OS6

 

[nightpilot]

I have an calibration problem with my Apple Watch Series 6 altimeter. It worked initially, then I noticed it was indicating 2100 feet too high, with a +/- 1650 feet error. If I un-pair and re-pair the watch, it corrects the problem (back to +/- 20 to +/- 40 feet error and the correct altitude displayed), then it goes bad after a day to two. Also, when I installed Watch OS 7.2, it corrected the problem for a day or so. Now it's back to 2100 feet too high.
I can see the altimeter working if I raise/lower my wrist a few feet or ride an elevator. It's just that the calibration is totally off (there is no temperature / pressure variation that would cause this error).
Talking to Apple via text chat or phone was a big frustration as I could not get to a person that understands how a barometric altimeter works.

 

[StumpyBloke]

I have an calibration problem with my Apple Watch Series 6 altimeter. It worked initially, then I noticed it was indicating 2100 feet too high, with a +/- 1650 feet error. If I un-pair and re-pair the watch, it corrects the problem (back to +/- 20 to +/- 40 feet error and the correct altitude displayed), then it goes bad after a day to two. Also, when I installed Watch OS 7.2, it corrected the problem for a day or so. Now it's back to 2100 feet too high.
I can see the altimeter working if I raise/lower my wrist a few feet or ride an elevator. It's just that the calibration is totally off (there is no temperature / pressure variation that would cause this error).
Talking to Apple via text chat or phone was a big frustration as I could not get to a person that understands how a barometric altimeter works.

Send an email directly to Tim Cook. That’s what I did and within 2 days I had a member of the UK executive team on the phone passing me on to a member of the tech team that you cannot get through to via other means.

For me, since the 7.2 update mine has been pretty good. Not sure if it’s a coincidence or not but I’ve now got the direct contact details for these higher level staff members if it goes wrong again.

 

[michaelb5000]

I think when folks say there is a discrepancy on the apple watch, that is when reading the current position in the elevation complication and/or the compass app? I agree that you can see readings in that display that are off by +/- 100 feet or more, and that is almost certainly caused by changes in pressure at your location related to weather. I have been tracking barometric pressure in an app on my phone and I can see the current elevation go up and down in direct relation to that. But I haven't seen any evidence that this impacts the actual function of the always on altimeter: tracking your elevation changes, either directly in the apple watches builtin "flights climbed" in the health data, or when the altimeter is used by any app on your watch that uses it, so altimeter apps or mapping and tracking apps (like WorkOutdoors). Those apps will report a different elevation position for you and will track different elevation when you are using them, then the values that displayed in the elevation complication or compass app. I agree this is a bug and that Apple will hopefully fix this.

At least so far, in my limited testing, the most likely way to get the apple watch complication to reset and calibrate itself is to drive somewhere, so 5-10 miles; with a big hill may be even better. I can't tell during the drive when it resets, so not usually on the way out, more likely on the way back, but that has reset the complication to correct value when I return. Driving to a trailhead in the mountains, may produce a similar effect. A button to reset or calibrate the altimeter to the current GPS value would be helpful since then we could do this manually.

If anyone is seeing errors in the altimeter position and has driven distances and gone up and down hills (preferably with your phone) and is not seeing this correct itself, then that would show this theory is not true or only partially true.

 

[StumpyBloke]

When my altimeter is wrong, those incorrect readings are also reflected in my workout statistics in the fitness app. For example, a common route that I take has an elevation difference of about 60 feet, but when the altimeter is playing up it can end up being thousands of feet. But as I say, so far with 7.2 it seems okay.

 

[StumpyBloke]

Just wondering if anyone, specifically in the UK perhaps, if they’ve noticed that their altimeter readings are becoming more and more inaccurate throughout the last day or so with them reading higher and higher. Mine is now 167 m out.

 

[Cheefy]

Just wondering if anyone, specifically in the UK perhaps, if they’ve noticed that their altimeter readings are becoming more and more inaccurate throughout the last day or so with them reading higher and higher. Mine is now 167 m out.

Yep - in Scotland here. Had my Series 6 for three days. Tried the Altimeter yesterday and it was about 200 mtrs out at my house. The correct altitude is 60 mtrs and the Compass App on my IPhone says 60 mtrs. Also Google Earth - 60 mtrs. I had updated to 7.2 on the 25th so I don’t know what the altimeter was like before I updated it. I spent ages on the Apple Support chat yesterday and they did remote analysis on my sensors - nothing found. Last night I completely reset the watch and afterwards it was even worse reading 380 mtrs instead of 60 mtrs. Today it is worse still - now reading 425 mtrs. This is nothing to do with “margin of error” or varying barometric pressure. It clearly isn’t working properly. I tried my watch down at the beach next to my pals Series 5 and hers said 5 mtrs - mine said 270 mtrs. This was one of the reasons that I bought this watch.

 

[StumpyBloke]

It’s absolute **** isn’t it? And thanks for confirming too. I’ll pass this on when I speak with Apple next.

I can see a pattern with mine, when the pressure drops the inaccuracy of the altimeter gets worse. It’s now showing me at over 320 m above what I should be and got worse over the last 48 hours as the pressure dropped.

I am liaising with a senior Apple engineer about this because it renders this new feature absolutely useless and not fit for purpose. Originally I sent an email to Tim Cook I was so frustrated with it. And of course he didn’t read it but in all fairness to Apple they did ring me up from the executive office within 48 hours. How the hell did this feature pass any qualitative tests?? The mind boggles. Apple’s QC has gone down the pan big style.

Edit: to add, I don’t suppose you know if the pressure has dropped in your area whilst the altimeter readings have been getting worse (getting higher)?

 

[Cheefy]

It’s absolute **** isn’t it? And thanks for confirming too. I’ll pass this on when I speak with Apple next.

I can see a pattern with mine, when the pressure drops the inaccuracy of the altimeter gets worse. It’s now showing me at over 320 m above what I should be and got worse over the last 48 hours as the pressure dropped.

I am liaising with a senior Apple engineer about this because it renders this new feature absolutely useless and not fit for purpose. Originally I sent an email to Tim Cook I was so frustrated with it. And of course he didn’t read it but in all fairness to Apple they did ring me up from the executive office within 48 hours. How the hell did this feature pass any qualitative tests?? The mind boggles. Apple’s QC has gone down the pan big style.

Edit: to add, I don’t suppose you know if the pressure has dropped in your area whilst the altimeter readings have been getting worse (getting higher)?

Yes the barometric pressure has dropped considerably and in line with what you said the accuracy has got much worse. As I do a lot of Munro climbing I rely on knowing what my altitude is so as it stands my AW 6 is not suitable in any way for my use. I find it quite incredible that there can be such an error. It would appear that the barometer sensor is overiding the GPS Coordinates elevation. My GPS is working perfectly and matching other bits of kit that I have. I’m no expert but the correlation between the barometer and GPS is either incorrect or is being affected by something. Exactly the same App on my IPhone works perfectly. As you say, as it is, it is not fit for purpose.