v) When you have obtained a sharp 45° null, mark the
ground there. Note that for accurate results, you should
mark the ground directly below the top edge of the
bottom of the receiver, in order to account for the
physical dimensions of the receiver box.
vi) Measure the distance between the two null marks
(Figure 9)
. By triangulation, this surface distance will
be the same as the depth to the center of the line. For
excavation or trenching purposes, this means that the
actual top of the pipe or conduit will be shallower than
the measured depth by half of the pipe’s diameter. For
example, for a 12-inch diameter pipe, the actual depth
to the top of the pipe will be 6 inches less than the
measured depth.
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