Kapro Prolaser Multi Beam Manuel D'utilisation page 23

5. Rotate the laser level 180°, position it so that the center
of the down plumb dot is on the point b, which has
already been marked, and allow it to level.
6. Mark the center of the upper plumb dot on the ceiling as
point a2. (See Figure 10)
7. The distance between points a1 and a2 marked on the
ceiling is an indication of the actual deviation of the line
between the plumb dots from the ideal plumb line.
The distance between a1 and a2, should not be more
than 4 mm, otherwise send the laser level to a qualified
technician for repair.
23