Proton affinities of H2O for 4 levels of theory calculated via
formula (*) in the tutorial (all values in kcal/mol)
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level of theory         /\E(ele)        /\ZPE          P(A)
-------------------------------------------------------------------
         HF/6-31G       -182.60          8.74         175.34 
-------------------------------------------------------------------
         HF/TZV         -176.71          8.61         169.58
-------------------------------------------------------------------
CCSD(T)//HF/6-31G       -182.93          8.74         175.67
-------------------------------------------------------------------
CCSD(T)//HF/TZV         -175.65          8.61         168.51
-------------------------------------------------------------------


Computation of corrections C1 and C2 (in kcal/mol)
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C1 = 169.58 - 175.34 = -5.76
C2 = 175.67 - 175.34 =  0.32

Hence we can estimate P(H20,CCSD(T)//HF/TZV) to be

P = P(H20,HF/6-31G) + C1 + C2 = 175.34 - 5.76 + 0.32 = 169.90

which has to be compared with the "true" value of 

P(H20,CCSD(T)//HF/TZV) = 168.51

and is therefore in good agreement!