Quel jour de la semaine ?

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Not Intersect([B3:AF27], Target) Is Nothing And Target.Count = 1 Then
    jour = Cells(2, Target.Column)
    mois = Month(Range("A" & Target.Row))
    annee = Year(Range("A" & Target.Row))
    JourReconstruit = DateSerial(annee, mois, jour)
    If JourReconstruit >= DateSerial(annee, mois + 1, 1) Then
        Range("A1") = "Jour Inexistant"
    Else
        Range("a1") = JourReconstruit 
    End If
End If
End Sub

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
 If Not Intersect([B3:AF27], Target) Is Nothing And Target.Count = 1 Then
    Range("a1") = DateValue(Target.Column - 1 & "/" & Cells(Target.Row, 1).Text)
 End If
End Sub

And Target.CountLarge = 1

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim an%, mois As Byte, jour As Byte
If Intersect(Range("B3:AF" & Rows.Count), ActiveCell) Is Nothing Or Not IsDate(Cells(ActiveCell.Row, 1)) Then Exit Sub
an = Year(Cells(ActiveCell.Row, 1))
mois = Month(Cells(ActiveCell.Row, 1))
jour = Cells(2, ActiveCell.Column)
[A1].NumberFormat = "dd/mm/yyyy"
[A1] = Application.Min(DateSerial(an, mois, jour), DateSerial(an, mois + 1, 0))
End Sub

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim an%, mois As Byte, jour As Byte
If Intersect(Range("B3:AF" & Rows.Count), ActiveCell) Is Nothing Then Exit Sub
On Error Resume Next
an = Year(Cells(ActiveCell.Row, 1))
mois = Month(Cells(ActiveCell.Row, 1))
jour = Cells(2, ActiveCell.Column)
[A1] = ""
[A1].NumberFormat = "dddd"
[A1] = CDate(jour & "/" & mois & "/" & an)
If [A1] = "" Then MsgBox "Jour inexistant..."
End Sub