Private Sub Calendar1_SelectionChanged(ByVal sender As System.Object, ByVal _
      e As System.EventArgs) Handles Calendar1.SelectionChanged
 
        Dim a As String
        Dim DatumDiff As Date = Calendar1.SelectedDate
 
        If DropDownList1.SelectedIndex = 0 Then
            DatumDiff = DatumDiff.AddDays(-7)
        Else
            DatumDiff = DatumDiff.AddDays(-14)
        End If
 
        TextBox1.Text = DatumDiff
 
 
    End Sub