title: JPGraph Second axis doesn't show any data
body: <p>I am still learning about JPGraph but it is a great tool but it is quite complex I found. 
  Anyway I can draw the graph with the X and Y axis formatted correctly but when I add the Y2 axis it add the scale on the right side but no data is displayed. </p>
  
  <p>All help gratefully received.</p>
  
  <p>Data: </p>
  
  <pre><code> [$chartXaxis    
    array (size=4) 
    0 =&gt; int 1456531200
    1 =&gt; int 1458345600
    2 =&gt; int 1460156400
    3 =&gt; int 1462057200][1]
  
    $chartYaxis
    array (size=4)
    0 =&gt; int 360
    1 =&gt; int 460
    2 =&gt; int 380
    3 =&gt; int 320
  
    $chartY2axis 
    array (size=4)
    0 =&gt; int 20
    1 =&gt; int 19
    2 =&gt; int 15
    3 =&gt; int 14
  </code></pre>
  
  <p>Code Extract:</p>
  
  <pre><code>//set up X axis count
      $n = count($chartXaxis);
      $xmin = $chartXaxis[0];
      $xmax = $chartXaxis[$n-1];
  //*******************************************************
  
      // Create the graph. These two calls are always required
      $graph = new Graph(500, 300);
      $graph-&gt;SetScale('datlin',0,0,$xmin,$xmax);
  
  // Setup the labels to be correctly format on the X-axis
      $graph-&gt;xaxis-&gt;SetLabelAngle(30);
  
      // The labels should be formatted at dates with "Year-month"
      $graph-&gt;xaxis-&gt;SetLabelFormatString('My',true);
  
      $graph-&gt;title-&gt; Set("Golf Scores Graph");
  
  // Add a X-grid
      $graph-&gt;xgrid-&gt;Show();
  
  // Create the linear plot
      $lineplot = new LinePlot($chartYaxis,$chartXaxis);
      $lineplot-&gt;SetColor('blue');
  
  // Add the plot to the graph
      $graph-&gt;Add($lineplot);
  
      $graph-&gt;SetY2Scale('lin');
      $lineplot1 = new LinePlot($chartY2axis);
      $lineplot1-&gt;SetColor('red');
      $graph-&gt;AddY2($lineplot1);
  
  //*******************************************************
      //set up filename
      $filename = "PersonChart".$PlayerKey.".png";
  
      // Get the handler to prevent the library from sending the
      // image to the browser
      $graph-&gt;Stroke($filename);
  </code></pre>