use CGI;
use GD::Graph::lines;
my $cgi = new CGI;
  my @data = ( 
            ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"],
            [undef,undef,undef,undef,undef,undef,undef,undef,undef,undef,undef,undef],
            [undef, undef, undef, undef, 13,  0,  undef,  200,  200,  180,  160,  260],
            [undef, undef, 22, 15, 7,  -10,  undef,  undef,  400,  600,  100,  -260]
        );
  my $graph = new GD::Graph::lines( 700, 400 );
  $graph->set(skip_undef => 1);
  my $gd = $graph->plot( \@data );
  
  print $cgi->header(-type => "image/png", -expires => "-1d");
  print $gd->png;