public function get_description() {
        $allhelp = array();
        if ($this->aggregation != GRADE_AGGREGATE_SUM) {
            $aggrstrings = grade_helper::get_aggregation_strings();
            $allhelp[] = $aggrstrings[$this->aggregation];
        }

        if ($this->droplow && $this->can_apply_limit_rules()) {
            $allhelp[] = get_string('droplowestvalues', 'grades', $this->droplow);
        }
        if ($this->keephigh && $this->can_apply_limit_rules()) {
            $allhelp[] = get_string('keephighestvalues', 'grades', $this->keephigh);
        }
        if (!$this->aggregateonlygraded) {
            $allhelp[] = get_string('aggregatenotonlygraded', 'grades');
        }
        if ($allhelp) {
            return implode('. ', $allhelp) . '.';
        }
        return '';
    }