Start 



Available data 

 in terms of Q 



Theory requires In 

 if a' and y' vary 



Design problem 

 requires Q 



because 



To solve problem, 

 convert back to Q, 

 using a' = 0.6 



rj ■ '- 65 rw 



Construct Ijj curve 



using a' =0.6 



y ' = l.65y w (quartz) 



Figure 2. Use of I, in present practice, 



