Are you 'Selecting' a column  of interest to sum?
And does the column stop at Col Z?

I can implement the "OFFSET" function but need a bit more detail on your intent.
Something like this:

Sum(RangeOfCellsOfInterest)

RangeOfCellsOfInterest is replaced by the offset function that defines the
range of interest as an Array:
Offset(BaseCell,DeltaRow,DeltaColumn,RowsToInclude,ColumnsToInclude)

So The final expression is this:
Sum(offset(BaseCell,DeltaRow,DeltaColumn,RowsToInclude,ColumnsToInclude))