Oh woe is me. I pasted the wrong code example in the message. This is what should have been there:

#!/usr/bin/perl -w
use Chart::Plot;
use strict;

my $img = Chart::Plot->new();
my @xdataset = qw(791.312 809.298 825.259 842.510 855.028 861.120 870.
+554 870.977 877.036 893.436 1060.006 1066.030 1081.967 1270.989 2211.
+105 2225.178 2239.090);
my @ydataset = qw(1383.8 1863.9 1247   2191.4 2101.2 624.96 552.55 105
+0.3 690.71 538.11 705.84 566.41 397.68 133.13 158.5 91.587 82.42);

$img->setData (\@xdataset, \@ydataset,  'nolines points');


$img->setGraphOptions ('horGraphOffset' => 75,
                        'vertGraphOffset' => 100,
                        'title' => 'Mass Spectrum',
                        'horAxisLabel' => 'mass/charge',
                        'vertAxisLabel' => 'intensity' );

open (WR,'>plot.png') or die ("Failed to write file: $!");
binmode WR;            # for DOSish platforms
print WR $img->draw();
close WR;
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Sorry to waste your time once again. R