Private Sub Worksheet_Change(ByVal R As Range)
If Intersect(R, [C1]) Is Nothing Or CStr([C1]) = "" Then Exit Sub
[C1].Select
If Application.CountIf([A:A], [C1]) Then _
MsgBox "Cette référence existe déjà !", 48: [C1] = "": Exit Sub
[A2].Insert xlDown, CopyOrigin:=xlFormatFromRightOrBelow
[A2] = [C1]
End Sub