title: jpgraph Double Y axis issue
body: <p>Hi so I've been struggling a good while to make the chart I want and I'm getting very close.</p>
  
  <p>First I have performance data of a stock portfolio that should be on YAXIS #1... That's good.
  Then I want a benchmark on YAXIS #2... The Line plot works, but the scale is weird :</p>
  
  <p><img src="https://i.stack.imgur.com/25MBn.png" alt="enter image description here"></p>
  
  <p>Notice how it starts at 50 and goes 10, 15, 20, etc... 
  The thing is the scale should be between 3400 and 3800 since that's the range of my data.</p>
  
  <p>Here is my code :</p>
  
  <pre><code>    &lt;?php // content="text/plain; charset=utf-8"
  require($_SERVER['DOCUMENT_ROOT'] . '/wp-blog-header.php');
  require_once ('jpgraph.php');
  require_once ('jpgraph_line.php');
  require_once ('jpgraph_date.php');
  require_once ('jpgraph_utils.inc.php');
  
  // Get a dataset
  $data = get_transient( 'daily_nav' );
  $ydata = $data[1];
  $xdata = $data[0];
  
  $data2 = get_transient( 'CAC40_history' );
  $ydata2 = array_reverse($data2[1]);
  $xdata2 = array_reverse($data2[0]);
  
  
  $dateUtils = new DateScaleUtils();
  list($tickPositions, $minTickPositions) = DateScaleUtils::GetTicks($xdata);
  
  // Setup a basic graph
  $width=800; $height=500;
  $graph = new Graph($width, $height);
  $graph-&gt;SetScale('datlin');
  
  $graph-&gt;SetYScale(0,'lin');
  $graph-&gt;SetYScale(1,'lin');
  
  $graph-&gt;SetMargin(60,20,40,60);
  $graph-&gt;xaxis-&gt;SetPos('min');
  $graph-&gt;xaxis-&gt;SetTickPositions($tickPositions,$minTickPositions);
  
  // Setup the titles
  $graph-&gt;title-&gt;SetFont(FF_GEORGIA,FS_NORMAL,16);
  $graph-&gt;title-&gt;Set('Performance vs. CAC40');
  $graph-&gt;subtitle-&gt;SetFont(FF_ARIAL,FS_ITALIC,10);
  $graph-&gt;subtitle-&gt;Set('graphique journalier depuis la création en juin 2012');
  
  // Setup the labels to be correctly format on the X-axis
  $graph-&gt;xaxis-&gt;SetFont(FF_ARIAL,FS_NORMAL,8);
  $graph-&gt;xaxis-&gt;SetLabelAngle(30);
  
  // The second paramter set to 'true' will make the library interpret the
  // format string as a date format. We use a Month + Year format m-d-Y
  $graph-&gt;xaxis-&gt;SetLabelFormatString('m-Y',true);
  
  
  // And then add line. We use two plots in order to get a
  // more distinct border on the graph
  $lp2 = new LinePlot($ydata,$xdata);
  $lp2-&gt;SetColor('#71a7da');
  $graph-&gt;Add($lp2);
  $graph-&gt;xgrid-&gt;Show();
  $graph-&gt;AddY(0,$lp2);
  
  // second chart
  $lp3 = new LinePlot($ydata2, $xdata2);
  $lp3-&gt;SetColor('blue');
  //$graph-&gt;Add($lp3);
  //$graph-&gt;xgrid-&gt;Show();
  $graph-&gt;AddY(1,$lp3);
  
  
  // And send back to the client
  $graph-&gt;Stroke();
  ?&gt;
  </code></pre>
  
  <p>Would be great if anyone can help, can't figure this one out.
  Thanks</p>