public function col_prevgrade(\stdClass $history) {
        if (!empty($this->gradeitems[$history->itemid])) {
            $decimalpoints = $this->gradeitems[$history->itemid]->get_decimals();
        } else {
            $decimalpoints = $this->defaultdecimalpoints;
        }

        return format_float($history->prevgrade, $decimalpoints);
    }