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8
3.3 CROSSED BARS
This refers to the common structure of one set of parallel bars running
vertically, and a second set running horizontally but not touching the
first set.
First map out the horizontal bars by holding the search head with the
handle horizontal, and scanning vertically along lines which run
between the vertical bars. When the sensitivity is reduced as
necessary, the horizontal bars will be resolved exactly as in the
previous example of parallel bars. Still keeping the handle horizontal,
repeat the vertical traverses, but try moving the search head vertically
up and down as well; it will be found the horizontal bars are clearly
resolved, regardless of whether the search head is also over a vertical
bar or not.
Now turn the search head so the handle is vertical, and scan horizontally. This time the vertical bars (and
the spaces between them) are clearly indicated, whilst the horizontal bars are largely ignored. (Note that if
the vertical bars are significantly different from the horizontal bars in either size or distance, the optimum
setting of the ZERO SET rotary control may also be slightly different).
To sum up: the maximum signal occurs when the search head is over a bar and aligned parallel to it; a
minimum (or null) signal occurs when the search head is in the centre of the space between bars, whatever
the alignment (at the crossing-points, a signal is obtained from each bar).
DISCONTINUED