Minelab F3 Mine Detector Operation Manual page 19

 During operation, continuous internal self-testing continues and
an alarm tone is triggered on detection of any fault condition
(refer to Section 3.3 for a description of the alarm tones).
 To turn the F3 off, slide the On/Off Switch away from the Handle.
b. Ground Balance/Audio Reset Button. Easily identifiable as the
Green Button located on top of the Handle, this dual action button
carries out the following functions:
 Ground Balance. A key feature of the F3 is its ability to detect
metallic mines in all ground conditions. False alarms due to
mineralised (magnetic/lateritic) soils are automatically removed
through use of the Ground Balance function.
 Audio Reset. On occasion, the Threshold Tone may become
louder than normal. Holding the coil stationary over a metallic
object or over mineralised ground for an extended period of time
may cause this. Also, if the detector is being used in the kneeling
position (shafts retracted), any movement of the coil relative to
the shaft may cause the Threshold Tone to increase. The
Threshold Tone can be returned to the normal volume level using
the Audio Reset function.
c. Noise Cancel Button.
 Interference from electrical motors, lights, power lines and other
detectors can occasionally cause the Threshold Tone to vary in
pitch and volume. When this occurs, the ability of an operator to
distinguish targets may be degraded.
 Using the Noise Cancel function, an operator can initiate an
automatic frequency scanning sequence resulting in the F3
selecting an operating frequency that minimises the effect from
interference.
d. Earset Socket.
 The F3 has an internal speaker located inside the Handle.
However, the F3 can also be fitted with an Earset via the Earset
Socket. The procedure for connecting the Earset is described at
Section 2.3.h.
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