Buick 1998 Century Owner's Manual page 292

To check the aim, the vehicle should be properly
prepared as follows:
0
0
0
0
0
0
0
Place the vehicle
on
a level pad or surface.
The vehicle should not have any snow, ice or mud
attached to it.
The vehicle should be fully assembled and all other
work stopped while headlamp aiming is being done.
There should not be any cargo or loading of the
vehicle, except it should have a full tank of gas and
one person or 160 lbs. (75 kg) on the driver's seat.
Close all doors.
Tires should be properly inflated.
Rock the vehicle to stabilize the suspension.
NOTICE:
To make sure your headlamps are aimed
properly, read all the instructions before
beginning. Failure to follow these instructions
could cause damage to headlamp parts.
For the vertical adjustment, state inspection stations
will generally allow a reading of plus 0.76 degrees or
minus 0.76 degrees from the center of the bubble.
It is recommended that the
upper limit not exceed
plus 0.4 degrees from the
center of the bubble.
Other drivers may flash
their high beams at you if
your adjustment is much
above plus 0.4 degrees.
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