Public Function DateToWeek(ByVal dDate As Date) As String
        ' Startdatum der ersten Kalenderwoche des Jahres und Folgejahres 
        ' berechnen
        Dim dThisYear As Date = CalendarWeek(1, dDate.Year)
        Dim dNextYear As Date = CalendarWeek(1, dDate.Year + 1)
 
        ' Prüfen, ob Datum zur ersten Woche des Folgejahres gehört
        If dDate >= dNextYear Then
            ' Rückgabe: KW 1 des Folgejahres
            Return dDate.Year + 1 & "01"
        ElseIf dDate < dThisYear Then
            ' Falls das Datum noch zu einer KW aus dem letzten Jahr zählt
            Return dDate.Year - 1 & DatePart(DateInterval.WeekOfYear, _
              New Date(dDate.Year - 1, 12, 28), FirstDayOfWeek.Monday, _
              FirstWeekOfYear.FirstFourDays)
        Else
            ' KW = Differenz zum ersten Tag der ersten Woche
            Return dDate.Year & Format$(dDate.Subtract(dThisYear).Days \ 7 + 1, _
              "00")
        End If
    End Function

  Private Sub btn_btn_Auswerten_Click(sender As Object, e As EventArgs) Handles _
    btn_Auswerten.Click
        Dim dt As DataTable = DSABLAGE.STATUSLM
        Dim year_selected As Integer = CInt(cbx_Jahr.SelectedItem)
        'Häufigkeitstabelle aus Datensätzen erstellen
        Dim dc As New DataTable
        With dc.Columns
            .Add("Month", GetType(String))
            .Add("Freq. done", GetType(Integer))
            .Add("Freq. todo", GetType(Integer))
        End With
 
        dc.PrimaryKey = {dc.Columns("Month")}
 
        For i As Integer = 0 To dt.Rows.Count - 1
            Dim dr As DataRow = dt.Rows(i)
            If DirectCast(dr("LMSTATUS"), Date).Year = year_selected Then
                'sortierbarer Jahr-Monat-String
                Dim ym As String = _
                 dr.Field(Of Date)("LMSTATUS").Year.ToString & "-" & _
                 dr.Field(Of Date)("LMSTATUS").Month.ToString("00")
 
                'Datensatzsuche nach Monat in Häufigkeitstabelle
                'gemäß Primärschlüssel     
                Dim dcr As DataRow = dc.Rows.Find({ym})
                If dcr Is Nothing Then
                    dcr = dc.Rows.Add({ym, 0, 0})
                End If
 
                Dim fcol As String
                fcol = dc.Columns(1).ColumnName
 
 
                'Häufigkeit bestimmen
                dcr(fcol) = CInt(dcr(fcol)) + 1
            End If
        Next i
 
        Dim bs As New BindingSource With {.DataSource = dc}
        bs.Sort = "Month ASC"
 
        'Chart für Häufigkeiten erstellen
        With Chart1
            .ChartAreas.Clear()
            .Series.Clear()
            .Legends.Clear()
            .AntiAliasing = AntiAliasingStyles.All
            .TextAntiAliasingQuality = TextAntiAliasingQuality.High
            .BackColor = Color.Transparent
            .BackSecondaryColor = Color.Transparent
            .BackHatchStyle = ChartHatchStyle.DashedHorizontal
            .BackGradientStyle = GradientStyle.DiagonalRight
            .BorderColor = Color.Transparent
            .BorderDashStyle = ChartDashStyle.DashDotDot
            .BorderWidth = 1
 
            .Titles.Clear()
            .Titles.Add("Titel")
            .Titles(0).Text = "LM - AUSWERTUNG"
            .Titles(0).Font = New Font("Thahoma", 10, FontStyle.Regular)
            .Titles(0).ForeColor = Color.WhiteSmoke
            .Titles(0).BorderColor = Color.Transparent
            .Titles(0).BackColor = Color.Transparent
            .Titles(0).Alignment = System.Drawing.ContentAlignment.BottomCenter
            .DataSource = bs
            'hier könnte man auch mittels IF Bedingung 3D <> 2D umschalten
            .ChartAreas.Add("Base").Area3DStyle.Enable3D = False
            'X - Achse
            With .ChartAreas("Base").AxisX
                .Title = "Jahr-Monat"
                .TitleForeColor = Color.WhiteSmoke
                .IsLabelAutoFit = True
                .LabelStyle.Font = New Font("Arial", 10)
                .LabelStyle.ForeColor = Color.WhiteSmoke
                .LabelStyle.Angle = -45
                .Interval = 1
            End With
            'Y - Achse 
            With .ChartAreas("Base").AxisY
                .Title = "Anzahl - Liefermangel"
                .IsLabelAutoFit = True
                .LabelStyle.Font = New Font("Arial", 10)
                .TitleForeColor = Color.WhiteSmoke
                .LabelStyle.ForeColor = Color.WhiteSmoke
            End With
 
            .Series.Add("LM")
 
            With .Series("LM")
                .XValueMember = "Month"
                .YValueMembers = dc.Columns(1).ColumnName
                .ChartType = SeriesChartType.StackedColumn
                .IsValueShownAsLabel = True
                .ChartArea = "Base"
 
            End With
 
 
        End With
    End Sub