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CHAPTER III. 



MEASUREMENT OF STANDING TREES. 



1. Ocular Estimate. 



ORIGINALLY, the volume of standing trees was estimated, 

 either merely by observation, or after having measured such 

 dimensions as could easily be ascertained, namely the diameter 

 and height. Such an estimate takes into consideration the 

 special shape or form of each tree, and fixes the volume 

 accordingly. 



The accuracy of purely ocular estimates depends entirely on 

 the person who makes them. To be only approximately 

 correct, the estimator requires great practice, and opportunities 

 to compare his estimates with actual measurements after the 

 trees have been felled. Even then the results are subject to 

 considerable errors, unless the estimator practises his art con- 

 stantly. Mistakes of 25 per cent, are of common occurrence, 

 and they may reach up to 100 per cent, in the case of an 

 inexperienced estimator. 



The uncertainty of absolutely ocular estimates led to the 

 measuring of diameter (or girth) and height ; this done, the 

 basal area near the ground can be calculated, multiplied by 

 the height, and an estimate made of the actual volume of 

 the tree. It stands to reason that such an estimate is less 

 dependent on the individuality of the estimator than that 

 mentioned above, since he has only to estimate the proportion 

 which exists between the actual volume and that of an 

 imaginary body constructed out of the height and the sectional 

 area at the base, a matter which he must decide according to 

 the peculiar form of the tree. By degrees it was considered 

 desirable to collect data regarding the form of various trees, 



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