<£,= true initial angle = 7" 



15° — 7° = 



22' 



(erroneous initial angle due to hypothetical 

 angular error in fetch front ) 



4>\ = true initial angle = 7" 

 <*o = - 7° + 15° = + 8° 



( erroneous initial angle due to hypothetical 

 angular error in fetch front ) 



FIGURE 3. POSSIBLE ERRORS IN CONSTRUCTION OF 4> ANGLES 



