5
MEASUREMENT OF HEIGHT
The actual measurement of the height
of the tree should be done from the
distance measured in the following
way: the observer sights the top of the
tree with both eyes open. The object
sighted, the hair line and the scale will
all be simultaneously visible in the
instrument`s field of vision. As soon
as the hairline coincides with the top
of the tree, the tree height can be read
off (in this example, from the 20 m
scale on the left of the instrument).
The reading obtained is the height of
the tree measured from the eye level
of the observer. The base of the tree
remains to be sighted. If this is
situated below the eye level of the
observer, then the actual height of the
tree is obtained by adding the two
readings together. If it is above the
observer`s eye level, the tree height is
obtained by taking the difference
between the two readings. In fact, in
the latter case the distance cannot be
measured horizontally. Thus, to get
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