SENSITIVITY
ADJUSTMENT
ELECTROMAGNETIC
INTERFERENCE
The principle use for the Sensitivity Control is to eliminate Electromagnetic Interference (EMI).
A hobby metal detector is an extremely sensitive device;
the search coil creates its own magnetic field and acts like an antenna. If your
detector beeps erratically
when the search coil is 
motionless, the unit is probably detecting another electromagnetic field.
Common sources of EMI are electric power lines, both suspended and buried, motors, and household appliances like computers and microwave ovens. Some indoor electronic devices, such as dimmer switches used on household lighting, produce severe EMI and can cause the detector to beep erratically. Other metal detectors also produce their own electromagnetic fields; so if detecting with a friend, keep two metal detectors at least 20 feet apart.
If the detector beeps erratically, REDUCE THE SENSITIVITY by pressing the Sensitivity ▼ Pad on the left of the control panel.
SEVERE GROUND CONDITIONS
A secondary use for the Sensitivity Control is to reduce false detection signals caused by severe ground conditions. While your Discovery 3300 contains circuitry to eliminate the signals caused by most naturally occurring ground minerals, 100% of all ground conditions cannot be anticipated. Highly magnetic soils found in mountainous and gold- prospecting locations can cause the detector to emit tones when metal objects are not present. High saline content soils and sands can sometimes cause the detector to false.
If the detector emits false,
MULTIPLE TARGETS
If you suspect the presence of deeper targets beneath a shallower target, reduce the sensitivity to eliminate the detection of the deeper targets, in order to properly locate and identify the shallower target.
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