Minelab F3Ci Operation Manual page 23

The Test Piece functional test must be conducted with the Sensitivity
Knob set to Position 4 (Default) and should be conducted whenever
the detector is switched on to confirm correct functionality of the
detector.
NOTE
After switching on the detector, the LEDs will always be disabled.
If an Earset Speaker OFF is connected to the detector, the LED
display will be automatically disabled for tactical reasons. However,
if required the LED display can be enabled by pressing the Mode
Select button and the Ground Balance button.
* WARNING *
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F3Ci Operations Manual