OBTAINING VERTICAL CONTROL OF PRACTICAL 

 VALUE WITH THE ABNEY HAND LEVEL. 



By William J. Paeth. 



Method and system become of more and more importance as 

 the work of Reconnaissance is done on a more intensive scale. 

 The object of the survey is to obtain, at all times, as much data 

 of standard value as possible, in a given time, and with the 

 amount of money allowed for the work. In order to approach 

 this ideal, the method and system of doing the work must be 

 adapted to the conditions encountered while doing each portion 

 of the work. Any one system will not result in this maximum 

 efficiency, at all times, and under all circumstances. 



Understanding, however, the nature and effect of the local 

 conditions under which the work is being performed, the method 

 and system can be chosen scientifically to meet the peculiar de- 

 mands of the situation, and this method and system should be 

 changed at will as soon as changing factors and influences war- 

 rant the use of another method. 



The maps obtained by cruising methods now employed vary 

 greatly in character and accuracy, depending upon the degree 

 of intensiveness with which the work is done. However, maps 

 of the greatest practical value and efficiency must be consistently 

 accurate within the limits of accuracy determined upon for the 

 type of map being made. To be consistently accurate the vertical 

 control and the horizontal control must be obtained with equal 

 degrees of precision. It would be out of place to obtain the 

 horizontal control accurately and to plot the vertical control 

 from less' accurate vertical location. A practically accurate forest 

 map is not always obtained unless all the factors affecting the 

 accuracy of the methods used are considered and understood. 



As stated before, methods must be chosen to fit local needs. 

 Circumstances may affect the balance in accuracy between verti- 

 cal and horizontal control and in order to make the map con- 

 sistently accurate new methods of obtaining either the horizontal 

 or vertical control must be adopted. To illustrate; the compass 

 man may be able to work within the prescribed limits of error 



