White’s Electronics Goldmaster GMT - Manual (Page 21)

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the detector is ground balanced, the (-) & (+)
controls are used only occasionally to update the
ground balance setting. Old workings and
outcroppings, however, can produce large ground
mineral variations that make detecting such areas a
little more challenging. Fast changing ground
mineralization and areas loaded with hot rocks are
better searched using the Fast Auto Trac Mode of
the GMT. Life will be easier and simpler.
A word about Overcorrecting when tuning for
Perfect Ground Balance:
At first you will overcorrect the Ground Balance.
For example, if the sound decreases as the coil
approaches the ground pressing the (+) button
compensates. At some point the decrease in sound
as the coil approaches the ground will diminish and
then the sound will shift and begin increasing as the
coil approaches the ground. This overcorrection is
expected and you can now switch to the (-) button
to find the point little or no change in threshold is
noted as the coil is pumped. You may overcorrect
again with the (-)button indicated by the sound
shifting back to decreasing as the coil approaches
the ground and indicating you need to return to the
(+) button to compensate. With practice over
shooting will be minimal and by jockeying back
and forth from (-) to (+) buttons you will be able to
quickly hone in on perfect balance.
An OPTIONAL method for Perfect GROUND
BALANCE:
Up till now we had described just one procedure for
manual GROUND BALANCE. That was to deter-
mine whether the sound gets softer or louder as the
coil approaches the ground. If the sound decreases
as the coil approaches the ground, press the (+)
button and if the sound increases as the coil ap-
proaches the ground, press the (-) button. The fact
is, whenever the sound decreases as the coil ap-
proaches the ground it will actually increase as the
coil is lifted away from the ground and vice versa.
Sometimes it is easier to hear an increase in sound
rather than a decrease in sound. If this is easier for
you, merely correct with the (+) pad if the sound
increases when the coil is lifted and correct with the
(-) pad when the sound increases on the down push.
The end results are identical (no audio change upon
either toward or away pumps of the searchcoil).
Use whichever method is easiest for you.
Problems from Low Ground Mineralization:
The GMT is designed to work in an environment of
heavy iron mineralization. In some instances there
may be so little mineralization that thesearchcoil
will never go quiet as it approaches the ground or
the Ground Balance pads seem to have little effect.
In other words, there never seems to be any change
or only a faint increase in hum as the coil is
pumped, regardless of the Ground Balance setting.
In this instance, merely set the number in the upper
left hand corner of the display (type of ground) to
"77" using the (+) & (-) touchpads.
Hot Rocks
The ever-present "hot rock" will always present
problems and must be contended with. It is our
belief that they should be recognized not necessar-
ily eliminated. Most large ones are on the surface
and can be kicked aside when identified. You will
soon learn what they sound like. The "overshoot"
or "boing" sound will soon become familiar. Fast
tracking is really a good option when they are
plentiful. We find it best to tune to the majority of
the ground matrix and learn what a "hot rock"
sounds like. The Fast Tracking of the GMT will
recover quickly upon leaving the vicinity of a "hot
rock" and will remain sensitive to gold nuggets.
Since there are different kinds of "hot rocks", it is
Chapter 5 GMT Searching