452 Forestry Quarterly 



of trails. These data should be converted to a unit basis of M 

 board feet per M feet of distance skidded ; and the average diameter 

 of the logs forming the trails computed on a uniform length ; that of 

 16 feet being used in this paper. The residts showing the time 

 required for skidding M feet of different diameters can be plotted as 

 points directly upon Fig. 2 and a curve drawn through these 

 points paralleling the curve shown for the corresponding type of 

 operation or class of timber, or it may be necessary to obtain the 

 average of groups of these points and plot the ctirve through the 

 new points. The reading from this curve in minutes or the time 

 unit employed should give the comparative time required for logs 

 of different diameters to pass through this stage of the operation. 

 The comparative cost can be obtained by substituting the cost per 

 tmit of time for this stage of the operation, and taking the com- 

 parative readings. 



There are no difficulties in computing mill sawing time per M 

 board feet and felling time. 



