<x 
FE 
a 
9° 
2 
observed 
theoretical 

102 
200 150 100 50 0 $0 100 180 200 250 
FEET 
250 
IN 
DISTANCE 
Fic. 6.—Comparison of observed and theoretical values for a magnetic north-south traverse across a 4,609-foot vertical string of casing. 
