GMC 1996 Sierra Owner's Manual page 107

To adjust for compass variance:
I . Use the CAL switch located at the bottom of the
mirror housing near the on/off switch. A safety pin
or paper clip can be used to press in the button. Press
and hold the CAL switch for five seconds until a
zone number appears in the display.
2 . Find your current location and variance zone number
on the following zone map.
3. Press the CAL switch on the bottom of the mirror
until the new zone number appears in the display.
After you stop pressing the button in, the display will
show a compass direction within a few seconds.
Outside Manual Adjust Mirror
Adjust your outside mirrors so you can just see the side
of your vehicle and have a clear view of objects behind
you. Some mirrors can be folded in to enter narrow
doorways
.
Power Remote Control Mirror (Option)
Select the mirror you want
to move by moving the
center of the switch, located
on the driver's door armrest,
to R (right) or L (left).
Then, adjust the mirror angle by pressing the outer
arrows on the switch until the mirror is ad-justed where
you want it.
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