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 $chart->add_series(
    categories => '=Sheet1!$B$1:$E$1',
    values     => "=Sheet1!\$B\$$variable:\$E\$$variable"
    );

 $chart1->add_series
   (
    values => "=Sheet1!\$B$6:\$$column_count$6",  
    name   => 'Test data series 1',
  );