title: Multiple axes on the same data
body: <p>I'm trying to have two axes on the same data. </p>
  
  <p>The data is a couple of <code>DefaultTableXYDatasets</code>. The plot is a <code>XYPlot</code>, and I have two <code>XYLineAndShapeRenderers</code> and one <code>StackedXYAreaRenderer2</code>. </p>
  
  <p>All data is in meters for the y-values, and I want to have one axis displaying it in meters and one axis displaying it in feet. Now this feels like a common thing to do, but I can't decide on the most obvious way to do it. One way that works would be to duplicate the data and have the y-values in feet, then add another <code>NumberAxis</code> and be done with it. </p>
  
  <p>But I thought it would be wiser to subclass <code>NumberAxis</code>, or inject some functionality into <code>NumberAxis</code> to scale the values. Or should I go with the first approach? </p>
  
  <p>What do you think? </p>