How do you code a sum function to allow variable input of a cell
address as one end of the cell range being summed? For example, in
cell A1, I want a formula like: =sum(xy:B5) where X can be either
hard coded as "B" or the result of a calculation or function that
returns the value of "B" and Y can be either hard coded as 1 or the
result of a calculation that returns the value of 1. Or where xy would
be the cell address resulting from either a horizontal or vertical
lookup function?