private function _writePlotSeriesLabel($plotSeriesLabel, $objWriter)
	{
		if (is_null($plotSeriesLabel)) {
			return;
		}

		$objWriter->startElement('c:f');
			$objWriter->writeRawData($plotSeriesLabel->getDataSource());
		$objWriter->endElement();

		$objWriter->startElement('c:strCache');
			$objWriter->startElement('c:ptCount');
				$objWriter->writeAttribute('val', $plotSeriesLabel->getPointCount() );
			$objWriter->endElement();

			foreach($plotSeriesLabel->getDataValues() as $plotLabelKey => $plotLabelValue) {
				$objWriter->startElement('c:pt');
					$objWriter->writeAttribute('idx', $plotLabelKey );

					$objWriter->startElement('c:v');
						$objWriter->writeRawData( $plotLabelValue );
					$objWriter->endElement();
				$objWriter->endElement();
			}
		$objWriter->endElement();

	}