where 
n 
ice vs tare 
peo 4 a > aie 
n ih 
KR=1 
Now approximate* Z' (7') by 
Z'=a WG) Pe (Gye ees +a.(P')+a_ (12) 
n-1 n-2 1 Oo 
Now, the several values of data points (7;,, 7;,) are substituted in 
equation (11) and for each (ies Zi), there will be a particular 
equation (12). There will be 7 such simultaneous equations in the 
nm unknowns: 
peteas) Claas) GL 
a io) 
Once these coefficients are determined, they can be put into equa- 
tion (12). This equation gives the interpolation for 7' values of 
Die 
Now we want to assign specific values to 7 and solve for the 
corresponding values of Z given by the above interpolation scheme. 
A direct substitution of equation (11) into equation (12) would result 
in a polynomial in Z. This would be difficult to handle, so the fol- 
lowing iterative scheme is used (fig. 11). Select 7=7,, one of 
the arbitrarily chosen isotherm values. Then, first, intersect 
*The harmonic series would probably give a better fit, but the 
transformation to the original coordinate system is rather intractable. 
