title: iOS-charts bar chart with negative values
body: <p>I am using the great iOS-charts pod for doing my graphics. Now I have to display a bar chart with y-value in a range from -120 to 0. When I add those values, I get the bars displays from the top - 0 - to the bottom.
  What I am looking for is a way to let the bar be drawn from the bottom of the chart up to it's value, because 0 means a lot for the application while -120 means nothing. So I would like to get a big bar for 0 and nothing for -120 like this.</p>
  
  <p>0</p>
  
  <pre><code> X
   X        X
   X   X    X
  </code></pre>
  
  <p>-120 x   X    X</p>
  
  <p>Any idea how I can achieve this behavior?</p>
  
  <p>Thanks a lot
  Andy</p>