Garrett Metal Detectors GTAx 550 Owner's Manual page 26

The Upper Scale of the graphic display will indicate
a detected target. This indication will remain for five
seconds or until a new target is detected (whichever
comes first). The Target ID Guide located above
the Graphic Display will help identify your detected
target.
When scanning, do not hurry. Walk at a pace
that is comfortable. Be methodical. Do not skip
any areas. Overlap each sweep at least 25%
of the searchcoil's width. Wear headphones for
greater sound perception and concentrate on your
scanning.
Erratic Sounds
When a metallic object is accepted, the detector's
speaker or headphone sound will increase from
your audio threshold level. Some rejected targets,
however, may cause the audio to "break up" or
sound erratic. This is generally a response to
shallow trash targets and can be remedied by
raising the height of your searchcoil when scanning.
Another indication of a reject target is an audio
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