Apple Watch May Display Incorrect Altitude Readings in Unusual Weather Conditions

[MacRumors]

The Apple Watch Series 6 and Apple Watch SE may give incorrect altitude readings in unusual weather conditions, as noted by iphone-ticker.de.

The Apple Watch Series 6 and Apple Watch SE feature a next-generation always-on altimeter to provide real-time elevation information. Apple says that its updated altimeter cross-references information from GPS and nearby Wi-Fi networks to detect even the smallest changes in elevation above ground level, up and down to the measurement of 1 foot.

However, a large number of Apple Watch users in Germany have been receiving altitude readings that were incorrect by a wide margin. Many users reported that their altitude was calculated 200 to 300 meters too high, despite the fact that affected devices had worked correctly in the past.

Users on Apple's German support forums found that a period of low air pressure was causing the Apple Watch's altimeter to give incorrect altitude readings. While it is normal for changes in air pressure to affect barometric altimeters, the problem is usually dealt with by regular recalibrations to the current air pressure value at sea level. However, Apple does not allow users to manually prompt altimeter recalibration, and it is unknown how often the Apple Watch automatically recalibrates itself.

Affected users should still receive correct information when tracking a workout such as a hike, since the Apple Watch records altitude relative to the start point. Nevertheless, it is not clear why some Apple Watches are not using GPS information to link barometric measurements to location. This would allow the Apple Watch to identify when there are fronts of weather that significantly affect air pressure and then prompt altimeter recalibration.

Some users in Germany are reporting that they are still receiving disproportionately incorrect readings, while others have found that the only way to prompt altimeter recalibration was to factory-reset their Apple Watch and iPhone.

Article Link: Apple Watch May Display Incorrect Altitude Readings in Unusual Weather Conditions

 

[jameswilby]

And there I was thinking I was going mad. Same for me... UK location fwiw

 

[chabig]

Part of the problem is that people think altimeters measure altitude. They really don't. They measure air pressure. To derive an altitude from pressure, you need outside information–typically the local atmospheric pressure. There are no doubt some tricks Apple could do to improve the altimetry using GPS position and altitude information, but those would have to be coded into the software. Maybe the altimeter will improve with subsequent iOS/WatchOS versions.

 

[4jasontv]

So that’s like three football fields?

 

[chabig]

So that’s like three football fields?

American or European?

 

[4jasontv]

American or European?

Do Europeans measure distance in sports venues?

 

[0128672]

Pack gear for Everest ascent
Pack Apple Watch and charger

 

[EugW]

I was surprised but my series 5 (not series 6) has been remarkably consistent for my house. It basically always says 110 m now, although initially it sometimes said 105 m. It has never said anything other than 105 or 110 m.

Is this because my house is a single fixed location, and WatchOS just remembers that? Or is the Series 6 proving to be inherently less accurate, if it's giving such widely discrepant readings?

 

[PinkyMacGodess]

Anything based on an altimeter is going to be inaccurate at times. It's working on pressure to tell altitude. Atmospheric pressure changes. It's why we have weather. GPS is more reliable, but it too is somewhat inaccurate depending on how it can, or can't, get signals to triangulate the position of the device at that moment. And this assumes that the port the altimeter uses itself isn't plugged.

This is a 'dog bites man' story, IMO. Someone upset that it's inaccurate really needs to be better informed how it works. *shrug*

 

[yaxomoxay]

here you go.. now I had to cancel the trip to climb the Himalayas.

 

[PinkyMacGodess]

Some may not know, but airplanes use a standard 'altitude' once they climb past 18,000 feet. When a plane is flying at 'flight level 350', that pilot needs to know that no one else was going to be flying at that same level due to inaccuracies in the physical measurement of air pressure, and that someone flying at flight level 340 is actually AT 34,000 feet, and not higher due to changes in weather and pressure. There are other regulations that cover flight level operations to try to keep passengers safe, and planes properly separated. To rely on physical altimeters would be incredibly dangerous.

Also plane altimeters are adjustable to compensate for local changes in atmospheric pressures. Imaagine taking off in stormy rainy low pressure areas like London England, and flying to the notoriously high pressure dominated Caribbean.

 

[subi257]

I have to admit to ignorance here...I had not realized the was even there. That is cool, I wonder if it would work in an airplane?

 

[PinkyMacGodess]

here you go.. now I had to cancel the trip to climb the Himalayas.

I think that's part of the reason why the highest mountains rise and fall over time. Well, aside from tecktonics, is because it's harder to measure absolute altitude at such extremes. Even GPS is an imperfect measure of the height (altitude) of the highest peaks which sounds weird...

 

[EugW]

I have to admit to ignorance here...I had not realized the was even there. That is cool, I wonder if it would work in an airplane?

It would not in a pressurized one.

 

[PinkyMacGodess]

I have to admit to ignorance here...I had not realized the was even there. That is cool, I wonder if it would work in an airplane?

It would show the artificial altitude the plane cabin is at (In a pressurized cabin), not the actual altitude the plane is flying at. Plus, given flight levels (see above) the actual altitude is not the same as the flight level, unless the atmospheric pressure is at 29.92 inHg.

In cabin pressure also varies by plane, airline, and route. That's why ears pop. That's why masks come down if there is a pressure drop. Humans can't breath for long at the altitude planes fly at.

 

[PinkyMacGodess]

It would not in a pressurized one.

And if you were in a non-pressurized one above about 10,000 feet, it wouldn't matter after a few seconds...

Cabin pressurization...

EDIT: Payne Stewart's pilots were incapacitated by hypoxia after a slow leak, apparently, caused a total loss of cabin pressure, and killed everyone on the plane in seconds to a minute. The plane flew on auto pilot until it ran out of fuel and crashed. That has happened several times over the years too. It was a tragedy, but they were dead long before the plane crashed, and probably had no idea it was happening. The pilots likely did, but were overcome before they could react. At altitude, the concentration of oxygen drops with the pressure. We need oxygen to survive.

 

[SuperCachetes]

Interesting. When I was playing with my new S6 last week, I did notice the elevation was sometimes off by 100 feet, and sometimes not. I shrugged it off because that feature wasn't really one of the selling points for me anyway.

Now I look at it, and sure enough there is the disclaimer "+/- 110 ft" which is a significant margin of error for someone nominally sitting around the 500' range. Ah well.

 

[grjj]

I have to admit to ignorance here...I had not realized the was even there. That is cool, I wonder if it would work in an airplane?

It'll work anywhere there's atmospheric pressure.
Most commercial airplanes are pressurized to about 7,000ft give or take a thousand. So you'd never see the plane's actual altitude with a barometric altimeter in the cabin.
Most commercial airplanes are also made of solid aluminum which is quite effective at blocking GPS signals. If you hold a GPS receiver up to the window you can get a fix, but as a passenger, pinpointing your exact location, altitude or speed is quite difficult with any instruments you may have with you.

 

[Blackstick]

South Florida checking in, "what?"

 

[nikaru]

Unpleasant situation...for a skydiver....

 

[nikaru]

And if you were in a non-pressurized one above about 10,000 feet, it wouldn't matter after a few seconds...

Cabin pressurization...

EDIT: Payne Stewart's pilots were incapacitated by hypoxia after a slow leak, apparently, caused a total loss of cabin pressure, and killed everyone on the plane in seconds to a minute. The plane flew on auto pilot until it ran out of fuel and crashed. That has happened several times over the years too. It was a tragedy, but they were dead long before the plane crashed, and probably had no idea it was happening. The pilots likely did, but were overcome before they could react. At altitude, the concentration of oxygen drops with the pressure. We need oxygen to survive.

There is plenty of air at 10k feet. At 20k feet it is good to have oxygen mask with you but you can still survive, no severe hypoxia is expected.

 

[WRChris]

I’ve also noticed the maps app on the watch shows a different eta than the app on the phone while used together. It’s been off by as much as 15 minutes and I have no idea why. The phone is usually accurate on its eta

 

[PinkyMacGodess]

Interesting. When I was playing with my new S6 last week, I did notice the elevation was sometimes off by 100 feet, and sometimes not. I shrugged it off because that feature wasn't really one of the selling points for me anyway.

Now I look at it, and sure enough there is the disclaimer "+/- 110 ft" which is a significant margin of error for someone nominally sitting around the 500' range. Ah well.

I remember playing with my Garmin Trek (something) GPS device once. It had an altimeter and also estimated altitude via GPS. It was often wrong, and the two methods rarely agreed. Heck, I was on my trainer with the same GPS, and the plot of my ride was all over the place. It looked like a sea urchin, spikes going everywhere. Getting that handlebar mount was a great way to spend money... Yikes...

 

[swingerofbirch]

Is it possible people are forgetting that their attitude and not their aptitude determines their altitude?

 

[PinkyMacGodess]

There is plenty of air at 10k feet. At 20k feet it is good to have oxygen mask with you but you can still survive, no severe hypoxia is expected.

Planes that have experienced a loss of cabin pressure dive to at or below 10,000 feet before the pilots can take off their oxygen masks. I was referring to that altitude in my comment. Yes, there is oxygen at even higher altitudes, but it's the percentage of oxygen, the volume (partial pressure) that they are looking for. Any hint of hypoxia can interfere with the brains functions, making snap decisions and evaluating emergency situations prone to be made in error. So while you are correct, the regulations, and physics, err on caution.