DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 5-6/1958 str. 69 <-- 69 --> PDF |
of height). Teschendorf´s and Stoffels´ theories are the logical ones and it is very likely that with careful and slow work results can be obtained according to this theory. But our experiment was carried out under conditions prevailing in practice when under the strees of measuring a great number of heights, there occurs a relaxing of attention. It is very likely that in this case the following occurs: first, the measurer equipped with Christen hypsometer sights through the lower and upper edge of the rule slot whereafter he once more controls these lines of sight and then he takes up reading in the line of sight to the staff top. This line of sight lying always within the lower half or quarter of the scale, the measurer, before reading off the staff top once more tries to sight the staff bottom exactly, and thus usually displaces the rule and spoils the line of sight to the tree top. Therefore the line of sight to the tree top is not equally accurate as the other two lines of sight. Stoffels´ theory assumes all three lines of sight to be equally accurate. If Stoffels´ formula is written in a rather more explicit form H If aH = / where 01, 02 and 03 are standard deviations of lines of sight on the rule referring to the tree top, tree bottom and staff top, and if oi is relatively large as compared to 02 and 03 in such way that the amounts comprising 02 and 03 — using at the same time a relatively large staff — may be neglected, we obtain a formula in which The same error due to fatigue appears also in Hub´s hypsometer. First, the measurer sights the staff without preliminarily bringing his head into the necessary position that — without an effort — he is unable to catch with his eye the line of sight to the tree top, and then he involuntarily rises also his head and reads off a too great height (see Fig. 3). This error is of systematic character while the error — due to fatigue — in the case of Christen hypsometer has a random character and therefore the Christen hypsometer is better and more suitable, if other sources of systematic errors are excluded. m> |