Private Sub tbRH65_KeyPress( _
  ByVal sender As Object, _
  ByVal e As System.Windows.Forms.KeyPressEventArgs) _
  Handles tbRH65.KeyPress
 
        Select Case Asc(e.KeyChar)
            Case 48 To 57, 8, 32
                ' Zahlen, Backspace und Space zulassen
 
            Case Else
                ' alle anderen Eingaben unterdrücken
                e.Handled = True
        End Select
    End Sub