Private Sub Worksheet_Change(ByVal Target As Range)
If Not Intersect([A2:D20], Target) Is Nothing And Target.Count = 1 Then
Application.EnableEvents = False
valsaisie = Target
Application.Undo
If Left(Target.Formula, 1) = "=" Then
Target.Formula = Target.Formula & "+" & valsaisie
Else
Target.Formula = "=" & valsaisie
End If
Application.EnableEvents = True
End If
End Sub