Perhaps something like this would work?

use strict;
use Statistics::Descriptive;
my $uwlRatio = 15;

my $poStat = Statistics::Descriptive::Sparse->new();
my $frStat = Statistics::Descriptive::Sparse->new();

while(my $line = <DATA>)
  {
    chomp $line;
    my ($poData, $frData) = split( m/\s/,  $line);
    $poStat->add_data($poData);
    $frStat->add_data($frData);


    if($poStat->mean() > 0)
      {
        my $pofrRatioMean = $poStat->mean() / $frStat->mean();
        if($pofrRatioMean > $uwlRatio)
          {
            print "DANGER WILL ROBINSON! PO/FR ratio out of spec!\n";
          }
        else
          {
            print "PO/Fr ratio within spec: $pofrRatioMean\n";
          }
      }
    else
      {
        print "not enough data to calculate ratio.\n";
      }
  }




__DATA__
0 0
0 0
150 10
0 0
200 40
210 40
220 40
220 30
220 20
220 10
220 05
220 01
220 100
220 100
2200 100
2200 2
2200 2
2200 1
[download]

With output like this:

$perl example.pl
not enough data to calculate ratio.
not enough data to calculate ratio.
PO/Fr ratio within spec: 15
PO/Fr ratio within spec: 15
PO/Fr ratio within spec: 7
PO/Fr ratio within spec: 6.22222222222222
PO/Fr ratio within spec: 6
PO/Fr ratio within spec: 6.25
PO/Fr ratio within spec: 6.77777777777778
PO/Fr ratio within spec: 7.57894736842105
PO/Fr ratio within spec: 8.51282051282051
PO/Fr ratio within spec: 9.59183673469388
PO/Fr ratio within spec: 7.09459459459459
PO/Fr ratio within spec: 5.85858585858586
PO/Fr ratio within spec: 9.11290322580645
PO/Fr ratio within spec: 13.4939759036145
DANGER WILL ROBINSON! PO/FR ratio out of spec!
DANGER WILL ROBINSON! PO/FR ratio out of spec!
[download]