I have a data set of three columns and 6000 rows, these columns represent the
last three months of sales actuals. In each column if a sale occurred then a
number is in the cell, if not then the cell is blank. In another column I
would like to perform a calculation using the most recent data. So if a sale
occurred in last month then a number will be in the appropriate cell and I
will use it, if the cell for last month is blank then I would like to use the
data from the previous month, and so on. I wrote some simple code, but it is
not working. The cell locations are correct as the data set is very large.

Sub Netback()
'
' Netback Macro
' Macro recorded 7/18/2008 by Sasol NA User

Range("bc81").Select
ActiveCell.Select

Do Until IsEmpty(ActiveCell([0], [-52]).Value)
ActiveCell.Offset(1).Select
If ActiveCell([0], [-13]).Value 0 Then
ActiveCell.FormulaR1C1 = "=R[0]C[-13]/R[0]C[-37]"
End If
If ActiveCell([0], [-13]).Value = IsBlank And ActiveCell([0],
[-14]).Value 0 Then
ActiveCell.FormulaR1C1 = "=R[0]C[-14]/R[0]C[-38]"
End If
If ActiveCell([0], [-13]).Value = IsBlank And ActiveCell([0],
[-14]).Value = IsBlank Then
ElseIf ActiveCell([0], [-15]).Value 0 Then
ActiveCell.FormulaR1C1 = "=R[0]C[-15]/R[0]C[-39]"
Else: ActiveCell.Value = 0
End If
Loop
End Sub

Help me find my obvious error.