title: extjs chart problem
body: <p>I am using ext do draw charts in the browser,I meet a problem:</p>
  
  <p>I want to draw two lines in one chart, so I use the ColumnChart, this is my data:</p>
  
  <pre><code>var store = new Ext.data.JsonStore({
      fields:['name', 'visits', 'views'],
      data: [
          {name:'Jul 07', visits: 245, views: 3000000},
          {name:'Aug 07', visits: 240, views: 3500000},
          {name:'Sep 07', visits: 355, views: 4000000},
          {name:'Oct 07', visits: 375, views: 4200000},
          {name:'Nov 07', visits: 490, views: 4500000},
          {name:'Dec 07', visits: 495, views: 5800000},
          {name:'Jan 08', visits: 520, views: 6000000},
          {name:'Feb 08', visits: 620, views: 7500000}
      ]
  });
  </code></pre>
  
  <p>Since the Visit data is much less than views.</p>
  
  <p>So the line which respresent the visit is too close to the xaxis, is there any idea?</p>
  
  <p><img src="https://i.stack.imgur.com/RzMjd.jpg" alt="alt text"></p>
  
  <hr>
  
  <p>Thanks for your reply, I decide to make them the same scale.
  BTW, I have another question,hope you can give some suggesion:</p>
  
  <p><img src="https://i.stack.imgur.com/zMarN.jpg" alt="alt text"></p>