Public Class Form1
 
    Private stopwatch As New Stopwatch
    Private elapsed As String
 
    Private Function GetElapsedTimeString() As String
        Dim elapsed As TimeSpan = Me.stopwatch.Elapsed
        Return String.Format("{0:00}:{1:00}:{2:00}:{3:000}", Math.Floor( _
          elapsed.TotalHours), elapsed.Minutes, elapsed.Seconds, _
          elapsed.Milliseconds)
    End Function
 
    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Timer1.Tick
        Label1.Text = GetElapsedTimeString()
    End Sub
 
    Private Sub btStart_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles btStart.Click
        Timer1.Start()
        Me.stopwatch.Start()
        btReset.Enabled = False
        btMark.Enabled = True
        btZero.Enabled = False
    End Sub
 
    Private Sub btStop_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles btStop.Click
        elapsed = GetElapsedTimeString()
        Timer1.Stop()
        Me.stopwatch.Stop()
        ListBox1.Items.Add(elapsed)
        Label1.Text = elapsed
        btReset.Enabled = True
        btMark.Enabled = False
        btZero.Enabled = True
        SaveListToFile(ListBox1, "C:\Users\Jan-Oliver.Deeg\Documents\Visual" & _
          "Studio 2010\Projects\ListBox1.txt")
    End Sub
 
    Private Sub btReset_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles btReset.Click
        Me.stopwatch.Reset()
        Label1.Text = "00:00:00:000"
        ListBox1.Items.Clear()
    End Sub
 
    Private Sub btMark_Click_1(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles btMark.Click
        ListBox1.Items.Add(GetElapsedTimeString)
    End Sub
 
    Private Sub btZero_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles btZero.Click
        Me.stopwatch.Reset()
        Label1.Text = "00:00:00:000"
    End Sub
 
    Public Sub SaveListToFile(ByVal ListBox1 As Object, ByVal Filename As _
      String)
        Dim file As New IO.FileStream(Filename, IO.FileMode.Create)
        Dim writer As New IO.StreamWriter(file)
 
        If ListBox1.Items.Count > 0 Then
            For i As Long = 0 To ListBox1.Items.Count - 1
                writer.WriteLine(ListBox1.Items(i))
            Next i
            writer.Close()
            file.Close()
        End If
    End Sub
 
End Class