Private Sub Worksheet_Change(ByVal Target As Range)
If Not Intersect(Target, [A:A]) Is Nothing Then
Select Case Left(Target, 4)
Case "T100"
Target.Offset(0, 3) = "BDF"
Case "T101"
Target.Offset(0, 3) = "MDT"
Case "T102"
Target.Offset(0, 3) = "FDR"
End Select
End If
End Sub