Garrett AT Max Manual page 13

Note: If the Ground Balance setting does not change during the
auto ground balancing process, the detector is either sufficiently
ground balanced already or the current ground exhibits such
neutral mineralization that the settings will not change.
Manual Ground Balance: Press and release the SHIFT button,
then press either the (+) or (-) MAN. GND BAL button, and
continually bounce (pump) the searchcoil from 1 to 8 inches (2 to
20 cm) above the ground. If low tones are produced, increase the
Ground Balance setting using the (+) MAN. GND BAL button. If
high tones are produced, decrease the setting using the (-) MAN.
GND BAL button. Press and release the (+) or (-) MAN. GND BAL
buttons to make single-step adjustments, or press and hold to
make large adjustments.
Continue bouncing the coil and making manual adjustments
until a minimum audio response is obtained, indicating the
detector is ground balanced. The Ground Balance setting will
be indicated on the LCD. The detector will automatically exit
the Manual Ground Balance mode after five seconds without a
button push. The Ground Balance setting will be retained when
the detector is switched OFF.
You may want to use the Manual Ground Balance function
to ground balance slightly positive to enhance detection of
small targets or balance slightly negative to reduce detection of
"hot rocks, " terra cotta and clay bricks. Adjusting the AT Max to
be ground balanced slightly positive may produce a weak but
audible response from the ground as the searchcoil is lowered.
Maintaining a level coil swing at a constant height above the
ground will minimize this ground response.
Typical Ground Balance Ranges:
80–99: Highly ferrous (magnetite, ferrous oxide minerals,
black sands, hot rocks, terra cotta)
24 Garrett Metal Detectors
60–80: Moderately mineralized soils (red clay, brown clay,
iron-bearing clay minerals, etc.)
20–60: Likely an iron object
0–20: Highly conductive, non-ferrous minerals such as
saltwater
Automatic Ground Balance Window™: Mineralized ground
is often a mixture or matrix of different soils, rocks, and pockets
of concentrated mineralization, each possibly requiring a
slightly different ground balance setting. In such cases it may
not be possible to find a single ground balance setting that
simultaneously balances to the different ground components.
This is not a result of limited ground balance resolution; rather, this
is due to localized variations in the ground minerals.
For conventional detectors operating in All Metal Mode, these
ground variations can produce false audio responses that reduce
the operator's ability to discern faint signals, resulting in missed
targets. Even detectors with continuous ground tracking cannot
compensate for these localized ground variations.
Garrett has addressed this issue with its Automatic Ground
Balance Window which effectively "spreads" the ground balance
setting in order to simultaneously ground balance to a range of
values. This smooths out the audio by reducing the subtle ground
responses and allows the operator to hear those faint targets.
This Window or "spread" automatically adjusts while performing
Auto Ground Balance. While in Ground Balance mode, the Ground
Balance Window setting is displayed as a two-digit number above
IRON DISC (see illustration on page 22). The first digit represents the
lower window setting and the second digit represents the upper
window setting, each digit ranging from 0 to 9. For example, with
Ground Balance set to 93.5 and a Ground Balance Window of 46,
the effective ground balance spread is from 93.5 minus 4 steps to
93.5 plus 6 steps (i.e. from 92.5 to 95.0).
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AT Max
™