Hi Dave,

With your N2, if N2/700 > 22 years, then modification is OK. Right?

Regarding my calculation, I will add step 0 and step 5a as folows:

0. Caculate Na1
5a. Check N1/Na1 + "my N2"/Na2 < 1

with:
N1 = 12600
"my N2" = 15400
Na2 from step 5