# what's wrong with my iPhone compass? **URL:** \ **Category:** Factual Questions\ **Created:** [May 12, 2016, 3:42am UTC](https://boards.straightdope.com/t/whats-wrong-with-my-iphone-compass/754591 "2016-05-12T03:42:29Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Mr\_Downtown](https://avatars.discourse-cdn.com/v4/letter/m/8e8cbc/32.png) [@Mr\_Downtown](https://boards.straightdope.com/u/Mr_Downtown)\ **Post date:** [May 12, 2016, 3:42am UTC](https://boards.straightdope.com/t/whats-wrong-with-my-iphone-compass/754591/1 "2016-05-12T03:42:29Z")
I just got a new (to me) iPhone 5, which I’m happy with. Except the compass shows north being in various random directions. I thought the compass app used GPS positioning rather than magnetism, which is why you have to “roll the ball around” a few times to get a reading in a new location. Maps can find me just fine, making me think the GPS module works fine (though it might be more reliant on cell tower positions than I realize). If ancient seafarers could have a north-pointing device in their pockets, why can’t I? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [May 12, 2016, 4:03am UTC](https://boards.straightdope.com/t/whats-wrong-with-my-iphone-compass/754591/2 "2016-05-12T04:03:39Z")
No, it uses a magnetometer, and is very sensitive to local magnetic fields. I had to give up a nice case, because it used magnets to hold the case shut. ---
**Author:** ![zombywoof](https://avatars.discourse-cdn.com/v4/letter/z/9e8a1a/32.png) [@zombywoof](https://boards.straightdope.com/u/zombywoof)\ **Post date:** [May 12, 2016, 4:05am UTC](https://boards.straightdope.com/t/whats-wrong-with-my-iphone-compass/754591/3 "2016-05-12T04:05:56Z")
> [@Mr\_Downtown](#): > > I just got a new (to me) iPhone 5, which I’m happy with. Except the compass shows north being in various random directions. > > I thought the compass app used GPS positioning rather than magnetism, which is why you have to “roll the ball around” a few times to get a reading in a new location. Maps can find me just fine, making me think the GPS module works fine (though it might be more reliant on cell tower positions than I realize). > > If ancient seafarers could have a north-pointing device in their pockets, why can’t I? If it’s like some GPS devices I’ve used, you might have to _move_ for some distance for it to be able to give you your heading as well as your location (and of course, you could always carry one of [these](http://www.amazon.com/SE-CC4580-Military-Lensatic-Sighting/dp/B001ID4ZY0/ref=zg_bs_219431011_1) in your pocket.) ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [May 12, 2016, 11:56am UTC](https://boards.straightdope.com/t/whats-wrong-with-my-iphone-compass/754591/4 "2016-05-12T11:56:50Z")
> [@Mr\_Downtown](#): > > I thought the compass app used GPS positioning rather than magnetism, which is why you have to “roll the ball around” a few times to get a reading in a new location. Maps can find me just fine, making me think the GPS module works fine (though it might be more reliant on cell tower positions than I realize). GPS-based compasses exist; they’re called [satellite compasses,](http://www.cactusnav.com/newsdesk_info.php?newsPath=17&newsdesk_id=16) and as you might expect, they’re immune to magnetic disturbances, but they also work everywhere on the earth, whereas magnetic compasses get flaky near the magnetic poles. But satellite compasses are large things with multiple GPS receivers separated by a distance of a couple of feet, and AFAIK their primary application is for boats, for which position _and_ orientation are important during docking/undocking. As has been noted, your phone’s compass senses the earth’s magnetic field. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 12, 2016, 9:54pm UTC](https://boards.straightdope.com/t/whats-wrong-with-my-iphone-compass/754591/5 "2016-05-12T21:54:27Z")
Right, GPS is based on the time delay from each satellite to the receiver. That won’t change for different orientations of any single receiver, so you can’t use it to find directions. If you have multiple receivers, like **Machine Elf** said, then you can use the position of both to find the direction between them. One advantage that you could get from a compass plus GPS vs. a compass alone is that the GPS could be built with a database of magnetic declination at various points on the Earth, so that once you determine magnetic north, you can instantly correct it to true north. ---
**Author:** ![andrewm](https://avatars.discourse-cdn.com/v4/letter/a/c57346/32.png) [@andrewm](https://boards.straightdope.com/u/andrewm)\ **Post date:** [May 13, 2016, 1:37am UTC](https://boards.straightdope.com/t/whats-wrong-with-my-iphone-compass/754591/6 "2016-05-13T01:37:16Z")
> [@zombywoof](#): > > If it’s like some GPS devices I’ve used, you might have to _move_ for some distance for it to be able to give you your heading as well as your location (and of course, you could always carry one of [these](http://www.amazon.com/SE-CC4580-Military-Lensatic-Sighting/dp/B001ID4ZY0/ref=zg_bs_219431011_1) in your pocket.) No. The iPhone compass is a magnetometer. It senses the earth’s magnetic field directly without needing to be moving.