Try this. I will say, that you are going to run into a problem of having too many x values for the width of the graph, then you need to adjust this x_label_skip value to condense it. A Tk canvas would be a nice way to do this. You could plot every value on a scrolled canvas, and scroll to the current time(or time of interest). Of course if it's for the web, Tk won't help. 
#!/usr/bin/perl
use warnings;
use GD::Graph::lines;
use strict;

my @time;
my @temp;
my @rad;

while(my $line = <DATA>){
 chomp $line;
 my ($celcius, $radiation, $time) = split(/ /, $line);
    push @temp, $celcius;
    push @rad, $radiation;
    push @time, $time;
 }

my $graph_data = [
           [@time], # X-values
           [@rad],  # Y-value 1
           [@temp], #Y-value 2 reference line
];

my $mygraph = GD::Graph::lines->new(600, 300);

$mygraph->set(
    transparent       => '0',
    bgclr             => 'white',
    boxclr            => 'lgray',
    fgclr             => 'white',
    x_label     => 'Time',
    y_label     => 'Value',
    title       => 'Temperature and Radiation',
    x_labels_vertical => 1,
#    x_label_skip => 1,
#    line_types  => [1, 1],
    line_width  => 2,
    dclrs       => ['blue', 'green'],
) or warn $mygraph->error;

$mygraph->set_legend_font(GD::gdLargeFont);

$mygraph->set_legend('Radiation','Temperature');

my $myimage = $mygraph->plot($graph_data) or die $mygraph->error;

open(GRAPH, ">$0.png");
print GRAPH $myimage->png;
close(GRAPH);
__END__
36 85 13:37
36 86 13:38
37 85 13:39
37 86 13:40
38 85 13:41
38 86 13:42
38 85 13:43
39 86 13:44
39 85 13:45
39 88 13:46
39 88 13:47
39 88 13:48
39 88 13:49
39 88 13:50
39 88 13:51
38 87 13:52
38 85 13:53
38 86 13:54
38 85 13:55
38 86 13:56
38 85 13:57
38 86 13:58
37 85 13:59
37 86 14:00
37 85 14:01
37 86 14:02
37 85 14:03
37 86 14:04
37 85 14:05
36 86 14:06
36 85 14:07
36 86 14:08

[download]
I'm not really a human, but I play one on earth. flash japh

In reply to Re^3: Help with GD::Graph by zentara
in thread Help with GD::Graph by jeiku

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.