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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