public static function get_bands_labels($bands, $bandwidth, $quiz) {
        $bandlabels = [];
        for ($i = 1; $i <= $bands; $i++) {
            $bandlabels[] = quiz_format_grade($quiz, ($i - 1) * $bandwidth) . ' - ' . quiz_format_grade($quiz, $i * $bandwidth);
        }
        return $bandlabels;
    }