Private oldTimeSpan As TimeSpan '<-------
 
    Private Sub Timer1_Tick(ByVal sender As Object, ByVal e As _
      System.EventArgs) Handles Timer1.Tick
 
 
        TS = oldTimeSpan + StoppUhr.Elapsed
 
        Label1.Text = Format(TS.Minutes, "00") & ":" & Format(TS.Seconds, "00") _
          & "." & Mid(Format(TS.Milliseconds, "000"), 1, 2)
 
    End Sub
 
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) _
      Handles Me.Load
 
        heutetag = Date.Today
        Label3.Text = Format(heutetag)
        Label2.Text = Format(TimeOfDay)
        Timer1.Interval = 20
 
        oldTimeSpan = My.Settings.klZeitpaket
 
 
        Label1.Text = Format(My.Settings.klZeitpaket.Minutes, "00") & ":" & _
          Format(My.Settings.klZeitpaket.Seconds, "00") & "." & Mid(Format( _
          My.Settings.klZeitpaket.Milliseconds, "000"), 1, 2)
 
    End Sub
 
 
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles Button2.Click
        'Button1.Visible = True
        'Button2.Visible = False
 
        StoppUhr.Stop()
        TS = oldTimeSpan + StoppUhr.Elapsed '<-------
 
        Timer1.Stop()
        endzeit = Now
 
        ' Label1.Text = Format(TS.Minutes, "00") & ":" & Format(TS.Seconds, 
        ' "00")
        My.Settings.klZeitpaket = TS
        Label1.Text = Format(TS.Minutes, "00") & ":" & Format(TS.Seconds, "00") _
          & "." & Mid(Format(TS.Milliseconds, "000"), 1, 2)
 
        My.Settings.Save()
        'ComboBox1.Visible = True
 
        '(d1.ToString("hh:mm:ss")
        ' d1 = d1.AddMinutes(50)
    End Sub

Gruß
Christoph