'Nur zum testen - sonst ohne Bedeutung
    Dim textbox1 As New TextBox With {.Text = "590"}
    Dim textbox2 As New TextBox With {.Text = "71,6"}
    Dim textbox3 As New TextBox With {.Text = "40"}
    Dim textbox4 As New TextBox With {.Text = "3"}
    Dim textbox5 As New TextBox With {.Text = "36"}
    Dim txtLänge As New TextBox
 
 
    ''' <summary>Berechnung der Speichenlänge, falls Formel korrekt !!!</summary>
    ''' <returns>Speichenlänge oder -1 bei Fehler</returns>
    Private Function ComputeFormulaX() As Double
 
        Dim ads As Double        ' Anzahl der Speichen (36)
        Dim adk As Double        ' Anzahl der Kreuzungen (3)
        Dim df As Double         ' Durchmesser Felge (590)
        Dim bn As Double         ' Breite Nabe (71.6)
        Dim lk As Double         ' Lochkreis Nabe (40)
        '
        Dim df2 As Double        ' 590^2
        Dim bn2 As Double        ' 71.6^2
        Dim lk2 As Double        ' 40^2
        Dim alpha As Double      ' cosinus
        '
        '
        If Not Double.TryParse(textbox1.Text, df) Then Return -1 ' 
        ' Innendurchmesser der Felge
        df2 = df * df                           ' df^2
        If Not Double.TryParse(textbox2.Text, bn) Then Return -1 ' Breite der 
        ' Nabe
        bn2 = bn * bn                           ' bn^2
        If not Double.tryparse(TextBox3.Text, lk) then Return -1 ' Lochkreis 
        ' der Nabe
        lk2 = lk * lk                           ' lk^2
 
        If Not Double.TryParse(TextBox4.Text, adk) Then Return -1 ' Anzahl der 
        ' Kreuzungen
        If Not Double.TryParse(textbox5.Text, ads) Then Return -1 ' Anzahl der 
        ' Speichen
 
        alpha = Math.Cos(720.0 * (adk / ads) * Math.PI / 180)   ' cosinus des 
        ' Winkels im Bogenmass
 
        Dim arg As Double = 0.25 * (df2 + lk2 + bn2) - (2 * df * lk * alpha)
        If arg <= 0 Then Return -1
        Return Math.Sqrt(arg)     
 
    End Function