my $tlsamples = @series_po; # = @series_fr
return 0 if ($tlsamples == 0);
my $sum_po = sum(\@series_po); # = 150
my $sum_fr = sum(\@series_fr); # = 10
 
$sum_fr = 1 if ($sum_fr == 0);
my $avg_po = $sum_po / $tlsamples; # =150 / 5 = 30
my $avg_fr = $sum_fr / $tlsamples; # = 10 / 5 = 2

$avg_fr = 1 (if $avg_fr == 0); # avoid div/0
my $pofr = $avg_po / $avg_fr; # = 15