Hello,

Lori's formula only works if values in A are increasing and if values
in B are decreasing (if B values are increasing we could drop the
"1-"). And its not extrapolating (ok, that was not asked for).

IMHO Lori's approach as well as Joe's one are outright dangerous,
Herbert's is a perfect 110% solution for this special case but he
documented his approach very well so that we can apply it generally, I
think.

Regards,
Bernd