Private Function VorherlBuchstabenKette(ByVal zahl As Integer) As String
      Dim sLetters As String = _
        "A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z"
 
      Return sLetters.Substring(0, zahl * 2 - 1)
   End Function