Apple iPhone 4G - Manual (Page 157)

Compass
20
Getting Compass Readings
The built-in compass shows which direction you’re facing, along with the geographical
coordinates of your current location. You can choose magnetic north, or have Compass
adjust the declination to show true north.
Important: The accuracy of the digital compass may be negatively affected by
magnetic or other environmental interference, including interference caused by the
close proximity of the magnets contained in the iPhone earbuds. The digital compass
should be used only for basic navigation assistance and should not be solely relied on
to determine precise locations, proximity, distance, or direction.
You need to calibrate the compass the first time you use it, and you may need to
recalibrate it occasionally after that. iPhone alerts you if calibration is needed.
Note: If location services is turned off when you open Compass, you may be asked to
turn it on. You can use Compass without turning on location services. See “Location
Services” on page 194.
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