F3 Operations Manual
36
b. STEP 2 Determine Centre of Target
In Step 1, the area of a target was determined. If the metal in
the target is sufficiently small, the area mapped will also be small
and therefore it is a relatively simple matter to pin-point the
centre of the target.
For larger targets, to determine the centre, the coil should be
slowly moved across the mapped area. As the coil approaches
the centre of the target, the threshold tone will increase to a
maximum volume (pitch may be high or low depending on the
composition of the metal). Where maximum volume is achieved,
the coil can be considered to be above the centre of the target.
Once confirmed, local Standard Operating Procedures should be
followed to mark the target.
Figure 24: Determining Target Centre
NOTE
An operator can confirm that the centre of a target has been located
by moving the coil slightly, in any direction, and returning to the
centre. In doing so the volume of the Threshold Tone should
decrease from maximum as the coil leaves the centre and return to
maximum as the coil returns to the centre.
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