Bosch GLL 50 Operating/Safety Instructions Manual page 27

– Mark the center of the vertical laser line at the floor of the door
opening (point I), at a distance of 16 ft (5 m) beyond the other side of
the door opening (point II) and at the upper edge of the door opening
(point III).
– Position the measuring tool on the other side of the door opening
directly behind point II. Allow the measuring tool to level in and align
the vertical laser line in such a manner that its center runs exactly
through points I and II.
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