protected function col_s($questionstat) {
        if ($this->is_calculated_question_summary($questionstat)) {
            list($min, $max) = $questionstat->get_min_max_of('s');
            $min = $min ?: 0;
            $max = $max ?: 0;
            return $this->format_range($min, $max);
        } else if (!isset($questionstat->s)) {
            return 0;
        } else {
            return $questionstat->s;
        }
    }