private function getSeriesLabel($rowLabel, $columnName)
    {
        $metricLabel = @$this->properties['translations'][$columnName];

        if ($rowLabel !== false) {
            // eg. "Yahoo! (Visits)"
            $label = "$rowLabel ($metricLabel)";
        } else {
            // eg. "Visits"
            $label = $metricLabel;
        }

        return $label;
    }