% 



.-/ 



^"^^-^^PARENT DIP TABLE. 



Numbers at top and bottom of vertical columnB represent true dip 

 angles (every 5° being given). Numbers to the right and left of 

 horizontal lines represent direttion angles (every 5° being given). 

 Each number in heavy faced type is the value c.f apparent dip 

 corresponding to the true dip and direction angle of the column and 

 line, respectively, in which it is situated. 



Numbers in h'nes in fine type give the difference (in decimals of 

 a degree) of apparent dip for each degi-ee of difference in true dip, at 

 the particular direction angle for the line conceme<L 



Numbers in columns in fine type give the difference (in decimals 

 of a degree) of apparent dip for each degree of difference in direction 

 angle at the particular true dip for the column concerned. 



These " difference numbers" permit interpolation of values not 

 directly given by the table. 



In performing this interpolation, correct first for difference of 

 true dip (at approximately the correct direction angle), and then 

 correct the result so obtained for difference of direction angle (at 

 approximately the correct true dip). 



For example: To find apparent dip when true dip is 63° and 

 direction angle 54°. Taking the 60° and 65° columns and the 

 50 and 55° lines we get the group of numbers: — 



48 12 54 



■7 6 



44J 1-3 51 



Difference in true dip is 3°. Since 54° is nearer 55" than 50°, take 

 the lower line. 



3x r3 = 3-9 to be added to 44J gives 48'4. 



Since 63° is about midway between 60° and 65° take '65 the mean 

 of '7 and '6 as the correction due to error of direction angle. 



■65 + 1 = -65 to be added to 48'4 = 49.05, i.e., 49° (in round 

 numbers) is the apparent dip required. 

 (Calculated by trigonometry the angle is 49°4). 



The values in the table are given to the nearest i° with a 

 probable error of ±J°. Hence the shght irregularities in difference 

 numbers. 



