$rx=101;

 $chart->add_series(
        name       => 'HISTOGRAM',
        categories => '=Sheet1!$A$1:$A$\$rx',   ## this works
        values     => '=Sheet1!$B$1:$B$\$rx',   ## does not work . get a blank chart . 
  
    );

$chart->add_series(
   
    categories => [ 'Sheet1', 1, 6, 0, 0 ],
    values     => [ 'Sheet1', 1, 6, 2, 2 ],
);