public static function get_graders($courseid) {
        global $DB;

        $ufields = get_all_user_name_fields(true, 'u');
        $sql = "SELECT u.id, $ufields
                  FROM {user} u
                  JOIN {grade_grades_history} ggh ON ggh.usermodified = u.id
                  JOIN {grade_items} gi ON gi.id = ggh.itemid
                 WHERE gi.courseid = :courseid
              GROUP BY u.id, $ufields
              ORDER BY u.lastname ASC, u.firstname ASC";

        $graders = $DB->get_records_sql($sql, array('courseid' => $courseid));
        $return = array(0 => get_string('allgraders', 'gradereport_history'));
        foreach ($graders as $grader) {
            $return[$grader->id] = fullname($grader);
        }
        return $return;
    }