192 Forestry Quarterly. 



To i^rove that the device is accurately made, the knot, d, should 

 be taken between the thumb and finger and a sight made on some 

 distant object across the pins e and /'. The apparatus should then 

 be reversed and the sight taken from f to e. If the two sights co- 

 incide, the object sighted at is on a level with the eyes of the 

 observer and the device is in working order. If the second sight 

 falls above or below the first sight, a point intermediate between the 

 two should be selected, and the lines ac and be so adjusted with the 

 screw eyes or staples at a and b that the desired result is obtained. 

 This last operation may require some patience as well as a little in- 

 telligence. 



If a ten per cent, down grade is desired, the sight should be from 

 e to h, or / to g. If the grade is up, the sight should be from h to e, 

 or g to /. If a fifteen per cent, grade is desired a pin should be 

 placed one and one-half inches from the upper pin on either vertical 

 line. To arrange the apparatus for any desired per cent, of grade, 

 taking it for granted that the distance between the parallel lines ei 

 and fj remains ten inches, the per cent, should be treated as a whole 

 number, one decimal place then pointed off, the result regarded as 

 inches and a pin inserted at that distance on the lines ei and fj, 

 measured from e and f respectively. 



In actual operation surprisingly accurate results have been obtain- 

 ed with this simple device. It is to be hojDcd it may prove of value 

 to some of the readers of the Forestry Quarterly. 



G. W. Peavy. 



