Cadillac 2002 DeVille Owner's Manual page 353

2. Measure the distance from the ground to the aim dot
on each lamp; if left low beam, subtract two inches.
Record this distance.
3. At the wall or other flat surface, measure from the
ground upward the recorded distance from Step 2
and draw or tape a horizontal line the width of
the vehicle.
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4. Turn on the low beam headlamps and place a piece
of cardboard or equivalent in front of the headlamp
not being aimed. This should allow only the beam of
light from the headlamp being aimed to be seen on
the flat surface.
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