use strict;
use GD::Graph::lines;

my @data = ( [1, 2, 3, 4, 5, 6, 7, 8, 9,],
         [ 8, 8.25, 8.5, 8.35, 8.76, 8.21, 8.6, 8.8, 8.5],
         [ 57.4, 57.6, 57.8, 57.9, 57.4, 58.5, 57, 57.87, 58.34] );

my $my_graph = new GD::Graph::lines (600, 400);

$my_graph->set(
    title => "My Graph",
    x_label => 'X axis label',
    y1_label => 'Y1 axis label',
    y2_label => 'Y2 axis label',
    boxclr => '#C0C0C0',
    two_axes => 1,
);

$my_graph->set_legend("data set 1", "data set 2");

my $gd = $my_graph->plot(\@data) or die $my_graph->error;
open(IMG, '>file.gif') or die $!;
binmode IMG;
print IMG $gd->gif;
close IMG;
[download]

Yes, you can have as many lines as you like, and they can all have different colours, patterns etc. I found the documentation for GD::Graph pretty useful.

If you could let us know what you've tried so far, we can probably help further.

Thanks, but I've just discovered how to do it. Just pass an extra array to the graph method apparently!

Cheers anyway!