Ford 1998 Crown Victoria Owner's Manual page 43

Controls and features
Press the control to turn the mirror
on or off.
The mirror will automatically return
to the normal state whenever the
COMP MIRROR
vehicle is placed in R
(Reverse)(when the mirror is on) to
ensure a bright clear view when
backing up.
ELECTRONIC COMPASS (IF EQUIPPED)
The compass reading will remain accurate during most driving
conditions. Unknown to the driver, the compass is continuously
recalibrating due to magnetic fields and subtle, slow changes in vehicle
magnetics which can occur over the life of the vehicle.
The compass reading will remain fixed when significant levels are
experienced (such as steel bridges). The compass will return to normal
operation upon leaving the magnetized area.
If highly magnetized items (such as magnetic mount antennas) are
placed very near the compass the display will change to "C" for 15
seconds, then display all segments until the magnetized item is removed.
Most geographic areas (zones) have a magnetic north compass point that
varies slightly from the northerly direction on maps. This variation is four
degrees between adjacent zones and will become noticeable as the
vehicle crosses multiple zones. A correct zone setting will eliminate this
error. Refer to Compass zone adjustment.
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