Private Sub Worksheet_Change(ByVal Target As Range)
If Not Intersect(Target, Range("c1:c20")) Is Nothing Then
Application.EnableEvents = False
Select Case Target.Value
Case Is = ""
Target.Offset(0, 2) = ""
Target.Offset(0, -2) = ""
Case Is = "NN"
Target.Offset(0, 2) = "NN"
Target.Offset(0, -2) = "NN"
End Select
Application.EnableEvents = True
End If
End Sub