Private Function Mean(ByVal dt1 As Date, ByVal dt2 As Date) As Date
 
        'Uhrzeit aussondern
        dt1 = dt1.Date
        dt2 = dt2.Date
 
        'das relativ frühere Datum ermitteln
        Dim dtmin As Date = dt1
        If dt2 < dtmin Then dtmin = dt2
 
        'absolute Differenz berechnen
        Dim ts As New TimeSpan(Math.Abs(dt1.Ticks - dt2.Ticks))
 
        'halbe Differenz in Tagen (auf ganze Tage gerundet) addieren
        Return dtmin.AddDays(CInt(ts.TotalDays) \ 2).Date
 
    End Function