THE CONTENTS OF LOGS AND TREES 177 



of i6-foot logs in the tree, which will give the board-foot 

 contents in the tree. 



Volume Tables. Foresters make use of volume tables in 

 estimating large tracts of timber. These give at once the 

 contents of a tree either in board feet or in cubic feet or other 

 unit when the height and diameter of the tree are known. 

 The diameter is always measured at breast height and is the 

 average of the largest and smallest diameters at that point 

 if the tree is not round. The height may either be the total 

 height of the tree or the merchantable length of the trunk. 

 Each volume table will specify which to use. The simplest 

 form of volume table is based on diameter alone. Volume 

 tables give average results, for the figures in volume tables 

 are found by averaging together the volumes of a large num- 

 ber of trees of the same height and diameter that have been 

 cut down and measured. They are intended for estimating 

 only a large number of trees. They are not to be used for 

 measuring the contents of an individual tree. Volume tables 

 give very accurate results when used for estimating large 

 stands of timber. 



Measuring the Diameters of Trees. The diameters of 

 trees are always measured at breast height or four and a half 

 feet above the ground. This point will be well above the flare 

 or swell usually found at the base of a tree. The trunks of 

 most trees are not perfectly round in cross-section, so that 

 two measurements are always taken at right angles to each 

 other and the average diameter used. 



The instrument used for measuring diameters of trees 

 is a wooden calipers. These can be purchased for a few dol- 

 lars. For estimating a small woodlot two carpenter's squares 

 placed end for end and the arms against the tree will measure 

 the diameter with great accuracy. Wooden calipers can easily 

 be made. 



Measuring the Heights of Trees. The heights of trees are 

 measured by instruments called hypsometers. These are of 



