3) Mark point a1 on the wall, in the middle of the
horizontal line at the left edge of the horizontal line
(see figure 5).
4) Turn the laser level counterclockwise until the right
edge of the horizontal line reach's near a1, mark a
point a2 on the wall in the middle of the horizontal line
(see figure 6).
16
a1
X
Figure # 5
x a1
x a2
Figure # 6
1.5m