This article originally appeared in TidBITS on 2013-10-18 at 1:27 p.m.
The permanent URL for this article is: http://tidbits.com/article/14204
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The iPhone’s Positioning Sensors Were Never Good

by Josh Centers

Much is being made of Gizmodo’s tests showing that the positioning sensors in the iPhone 5s are off [1]. Not just a little off, but off in a non-trivial way. The gyroscope read 3 degrees off, the compass 8 to 10 degrees off, and even the accelerometer seemed to be inaccurate.

There was only one problem with Gizmodo’s experiment: they only compared the iPhone 5s against the previous iPhone 5. That may have seemed reasonable at the time, but it assumes that the iPhone 5’s positioning sensors were accurate. Testing by TechHive [2] in a variety of locations with an iPhone 4S, 5, 5c, and 5s now shows that the iPhone’s positioning sensors have never been any good.

While TechHive didn’t find anything wrong with the iPhone’s leveling capabilities, none of the iPhone compasses matched up — to themselves, to each other, or to an inexpensive Suunto A-10 recreation compass. Some were off as much as 20 degrees, and the worst deviation came in three different iPhone 5 units. TechHive also tested the compass of the Android-powered LG G2 smartphone and found that it was the closest to the Suunto, off by only 3 to 4 degrees. (The question this result raises is if the Suunto was itself accurate; a single cheap magnetic compass might not have been the best control.)

While Apple could, and should, make the iPhone positioning sensors more accurate and consistent, the moral of the story is to not rely on smartphone sensors for critical tasks. As our own Rich Mogull said during our staff discussion, “As a mountain rescue guy, digital compasses make me nervous. I have enough trouble keeping a physical compass calibrated and accurate. You walk out of an office building in a city near power lines, and no compass will be accurate. It’s just physics. Indoors? Not a chance.”

It’s also worth noting that despite the fuss surrounding this story, we’re not hearing from users about losing an orienteering race due to incorrect compass readings (iPhones wouldn’t be allowed anyway), having a woodworking project be tippy because of issues with the iPhone’s level, or even having trouble playing accelerometer-based games. In short, despite the proven problems, the iPhone’s positioning sensors still work sufficiently well for the uses that most people demand of them.

[1]: http://gizmodo.com/the-iphone-5s-motion-sensors-are-totally-screwed-up-1440286727
[2]: http://www.techhive.com/article/2055380/six-iphones-tested-and-they-cant-agree-on-true-north.html