Ironside Prolaser 3D All-Lines Mode D'emploi page 19

3) Set up the laser on a tripod or on a solid surface in front of the wall,
at a distance of approximately 2 meters.
4) Unlock the pendulum and press the button to project the vertical
forward beam (#4) towards the plumb line.
5) Turn the laser, so the vertical beam will merge with the plumb line
below the hanging point.
6) Mark point a2 on the wall, in the middle of the vertical beam at the
same height as a1. (see figure # 6).
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