Minelab F3 Mine Detector Operation Manual page 27

If more than one LED is illuminated or the display is erratic (in
combination with a variable tone response), conduct Audio Reset
and/or Noise Cancel.
Small/deep target response
Large/shallow target response
Test Piece Procedure
at V/S default setting with Black Endcap
Up to three LEDs illuminated
Figure 14: Typical LED Responses
NOTE
Medium target response
Low Battery Alarm
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