Chart-Ajustement de l'axe de date

Bonjour

Je me demande comment modifier l'interval de l'échelle de la date , soit en mois (tout les 1er), soit au trois mois ou à la semaine?

voici mon modeste bout de code
Code:
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Private Sub FaireGraph(ByVal Data As DataTable, ByVal Str As String)
        Chart1.ChartAreas.Clear()
        Chart1.Series.Clear()
        'Dim ChartArea1 As New ChartArea()
        Chart1.ChartAreas.Add("ChartArea1")
        Chart1.Series.Add("Prix")
        'Type de graphique
 
        Select Case TSCBoxGenreGraph.SelectedItem
            'Ajustement des propriétés du graphique
            Case Is = "Air"
                Chart1.Series("Prix").ChartType = SeriesChartType.Area
                'Couleur du graphique
                Chart1.ChartAreas(0).BackColor = My.Settings.CouleurFond
                Chart1.ChartAreas(0).AxisX.MajorGrid.LineColor = My.Settings.CouleurAxe
                Chart1.ChartAreas(0).AxisY.MajorGrid.LineColor = My.Settings.CouleurAxe
                'Chart1.ChartAreas(0).AxisX.Crossing = Data.Rows.Count
                'Chart1.ChartAreas(0).AxisY.IsMarksNextToAxis = True
                Chart1.Series("Prix").Color = Color.FromArgb(128, Color.Aqua)
                Chart1.Series("Prix").BackSecondaryColor = Color.FromArgb(128, Color.Yellow)
                Chart1.Series("Prix").BackGradientStyle = GradientStyle.TopBottom
                Chart1.Series("Prix").BorderColor = My.Settings.CouleurLigne1
                Chart1.Series("Prix").BorderWidth = 4
            Case Is = "Ligne"
                Chart1.Series("Prix").ChartType = SeriesChartType.Line
                Chart1.ChartAreas(0).BackColor = My.Settings.CouleurFond1
                Chart1.ChartAreas(0).AxisX.MajorGrid.LineColor = My.Settings.CouleurAxe
                Chart1.ChartAreas(0).AxisY.MajorGrid.LineColor = My.Settings.CouleurAxe
                'Chart1.ChartAreas(0).AxisX.Crossing = Data.Rows.Count
                Chart1.Series("Prix").BorderColor = My.Settings.CouleurLigne1
                Chart1.Series("Prix").BorderWidth = 4
        End Select
        'Chargement du graphique
        Dim Prix As Double = 0
        Dim DaGra As Date = Nothing
        Dim HMax As Double = 0
        Dim BMax As Double = 0
        Dim EcartHB As Double = 0
        Dim Serie1 As New Series
        Serie1.Name = "Prix"
        Serie1.ChartArea = "ChartArea1"
        For y As Integer = 0 To Data.Rows.Count - 1
            DaGra = CDate(Data.Rows(y).Item(0)).ToShortDateString
            Prix = Data.Rows(y).Item(9)
            If y = 0 Then
                HMax = Prix
                BMax = Prix
            End If
            If Prix > HMax Then
                HMax = Prix
            End If
            If Prix < BMax Then
                BMax = Prix
            End If
            Chart1.Series("Prix").XValueType = ChartValueType.DateTime
            Chart1.Series("Prix").Points.AddXY(CDate(DaGra).ToShortDateString, Prix)
        Next
        'Ajustement de l'axe du prix
        '-----------------------------
        EcartHB = HMax - BMax
        If EcartHB > 0.12 Then
            EcartHB = EcartHB / 6
        End If
        Select Case EcartHB
            Case 0 To 0.2
                'Console.WriteLine(EcartHB.ToString & " " & 0.2)
                EcartHB = 0.02
            Case 0.21 To 0.5
                'Console.WriteLine(EcartHB.ToString & " " & 0.5)
                EcartHB = 0.5
            Case 0.51 To 1
                'Console.WriteLine(EcartHB.ToString & " " & 1)
                EcartHB = 1
            Case 1.01 To 5
                'Console.WriteLine(EcartHB.ToString & " " & 5)
                EcartHB = 5
            Case 5.01 To 10
                'Console.WriteLine(EcartHB.ToString & " " & 5)
                EcartHB = 10
            Case Is > 10.01
                'Console.WriteLine(EcartHB.ToString & " " & 10)
                EcartHB = 20
        End Select
        Dim FloorGr As Double
        If BMax < EcartHB Then
            FloorGr = 0
        Else
            Dim Intnbr1 As Integer = System.Math.Floor(BMax / EcartHB)
            FloorGr = Intnbr1 * EcartHB
        End If
        '---------------------------------
        'Ajustement de l'Axe de la date
        '???????
 
 
 
        Chart1.ChartAreas(0).AxisY.Interval = EcartHB.ToString("0.00")
        Chart1.ChartAreas(0).AxisY.Minimum = FloorGr.ToString("0.00")
 
    End Sub
merci de votre aide

mario