102 DETERMINATION OF THE INCREMENT. 



sufficient number of woods of various ages have been selected, 

 normal sample plots are measured in them, and the data worked 

 up into a yield table for the corresponding quality class. The 

 same procedure is followed for all other quality classes. 



Various authors have gradually elaborated this system, first 

 Seutter as early as 1799, then Hossfeld in 1823. Huber, in 

 1847, was the first to give a regular method of working with 

 an indicating wood. He calculated the mean tree of a normal 

 mature wood, analysed it and searched for younger normal 

 woods, the mean tree of which possesses the same dimensions 

 as the mean tree of the mature wood at the same time. His 

 method is, however, wrong, because the mean tree of the 

 mature wood was not the mean tree at all former stages of life. 



Theodor Hartig, and afterwards Robert Hartig, analysed only 

 the largest trees of the mature wood, and then searched for 

 younger woods, an equal number of the largest trees of which 

 show the same dimensions as the largest trees of the mature 

 wood had at the same age. Such woods are considered as 

 having been produced on localities of the same quality, so that 

 the} r can be united into one yield table. 



The system presupposes that the largest trees of the mature 

 wood were at all times amongst the largest trees at previous 

 periods of the wood's life. Although this holds good generally, 

 exceptions occur. Besides, the method is very troublesome in 

 execution. 



ii. BAUR'S METHOD OF PREPARING YIELD TABLES. 



After a sufficient number of normal sample plots on all sorts 

 of qualities have been carefully measured (at least 30 for each 

 desired quality class), the volumes are marked as ordinates 

 over the corresponding ages as abscissa (see figure 36). 



Next two curves are drawn, so that the lower touches the 

 lowest points, and the upper the highest points indicating these 

 volumes. Then the area thus confined is divided into as many 

 equal strips, as there are quality classes to be distinguished. The 

 woods falling into each strip are considered as belonging to 



