private function _getMark($mark)
    {
        switch (strtoupper($mark))
        {
            case "SQUARE": return MARK_SQUARE;
            case "UTRIANGLE": return MARK_UTRIANGLE;
            case "DTRIANGLE": return MARK_DTRIANGLE;
            case "DIAMOND": return MARK_DIAMOND;
            case "CIRCLE": return MARK_CIRCLE;
            case "FILLEDCIRCLE": return MARK_FILLEDCIRCLE;
            case "CROSS": return MARK_CROSS;
            case "STAR": return MARK_STAR;
            case "X": return MARK_X;
            default: return 0;
        }
    }