Why does the iPhone's compass require regular calibration?
May 19, 2014 12:22 PM   Subscribe

Why does the iPhone's compass require regular calibration?

The iPhone compass seems to require calibration before every (or nearly every) use. This makes it fairly useless for interactive wayfinding.

Of course, plain old analog compasses don't require such calibration. So what is it about a digital compass that makes it so hard to keep it calibrated?

I am asking mostly to satisfy my curiosity, but if you know of a way to fix or work around this problem, I'd love to hear it.
posted by enn to Technology (4 answers total) 3 users marked this as a favorite
The phone contains a number of Hall effect magnetometers that pick up all magnetic fields in the environment, no matter the source. The calibration motion helps it figure out which of these is the earth’s magnetic field, so it can ignore the others. I don't think there's any way to get around that.
posted by effbot at 12:56 PM on May 19, 2014 [1 favorite]

I think it's not so much than plain old analog compasses don't require calibration, as that they really can't be calibrated even if you wanted to.

In the wilderness, without many sources of magnetic fields other than the earth, they won't lead you far astray. But if you happen to be standing next to some big hunk of iron or DC power supply, you can't really trust your plain old analog compass. You probably can't trust your iphone compass either, but the iphone probably at least knows enough to figure out that, eg, north isn't straight down toward your toes. (Though I suppose doing your best to hold your plain old analog compass level, so that it can't respond to vertical field lines, should count as a "calibration motion" in a sense.)
posted by OnceUponATime at 1:10 PM on May 19, 2014 [1 favorite]

Analog compasses don't demand that calibration, but they also don't work accurately around large bits of metal or magnetic fields, but the iphone compass does.
posted by rockindata at 1:10 PM on May 19, 2014

For the record, some analog compasses can be calibrated -- see, for example, this NGIA manual (pdf). From my layman's understanding, the idea is to point the vessel at known directions (based on either landmarks or sun's position or something), record the deviations, and adjust your Flinder's bar and/or Kelvin's balls (if possible) or record deviations on your deviation card.
posted by mhum at 3:47 PM on May 19, 2014

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