Sub AverageRank()
Dim mainSheet As Worksheet
Dim iRow As Integer
Dim lastRow As Integer

'Set reference to the worksheet
Set mainSheet = Worksheets(1)
With mainSheet
     lastRow = Range("ranks").Rows.Count
     
'Compute average Amazon sales rank for book 1 within date range
     Cells(Range("ranks").Rows.Count + 620, 1).Select
     ActiveCell.Formula = "Average"
     ActiveCell.Offset(0, 1).Activate
     ActiveCell.Formula = "=Average(b618:b" & lastRow & ")" & ""
End With

End Sub
