private function _writeRecalcId()
	{
		$record = 0x01C1;    // Record identifier
		$length = 8;         // Number of bytes to follow

		$header = pack('vv',  $record, $length);

		// by inspection of real Excel files, MS Office Excel 2007 writes this
		$data = pack('VV', 0x000001C1, 0x00001E667);

		return $this->writeData($header . $data);
	}