MAGNETIC METHODS 



153 



which is a function of the geographic location of the station, with reference 

 to the base station used. It is appHed on a mileage basis, and for the area 

 here considered the earth's field increases 11.8 y's per mile to the north 

 (called + to the north, — to the south) and 4.7 y's per mile to the east, 

 (+ to the east, — to the west). + denotes an increase of the field and 

 — a decrease. 



The base station has, of course, zero L. and L. correction, (sometimes 



