Bosch GLM 40 User Manual page 18

CAUSE
Wrong reference point set.
Obstruction in path of laser beam.
The indication remains unchanged or the measuring tool
reacts unexpectedly after pressing a button
Software error.
The measuring tool monitors the correct function for each
measurement. When a defect is determined, only the
symbol shown aside flashes in the display. In this case, or
when the above mentioned corrective measures cannot
correct an error, have the measuring tool checked by an
after-sales service agent for Bosch power tools.
CORRECTIVE MEASURE
Select reference
corresponds to measurement.
Laser point must be completely on
target surface.
Remove the batteries and start
the measuring tool again after
reinserting them.
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point that