Makita DWD181 Instruction Manual page 182

Operation
The correct detection may be prevented
when the buried object and the scanner
are not positioned in parallel.
When how iron bars are placed in
concrete is unknown, scan in more than
one direction.
The correct detection may be prevented
when the buried object is right in front of
the scanner and in parallel to the scan
direction.
In that case, scan at more than one
position.
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