278 



DEEP BOREHOLE SURVEYS AND PROBLEMS 



A table of natural cosines and another of natural versines 

 should be kept, the latter being the simpler to use having 

 least multiplying figures. A check on each of these 

 methods would be always advisable; e.g., in a 200-ft. hole 



Fig. 186.- 



-190 

 -3100 



-Alignment chart for determining vertical corrections in crooked 

 holes. 



5 deg. off the vertical the cosine rule will give a correct 

 vertical distance of 199.24 ft. and the versine rule will 

 give the same. Table IX^ shows tabulated data, the 

 results of several such examples as the above. 



Plate XVII shows Milliken's chart^ for the graphic 

 determination of vertical corrections in crooked holes. It 

 is drawn on logarithmic paper, the off-vertical angles being 



^ By the courtesy of R. Van A. Mills, of Petroleum Engineering. 

 2 Charles V. Milliken, of the Amerada Petroleum Corporation, in Oil 

 Gas Jour., p. 102, 1930. 



