title: Ext JS 4.1.1 - Summary Grid - How to Calc a Summary Column Using Other Values in Summary Row
body: <p>I have a summary grid that sums the values of two basic number columns but I want the next column in the summary row to show a calculation containing the values of the sums in the first two columns. Specifically, I want a Percent Change summary that reflects the change between the sums of the first two columns. </p>
  
  <p>Here's a snippet of my grid with the three columns I'm talking about:</p>
  
  <pre><code>    xtype: 'numbercolumn',
      dataIndex: 'lastYearWages',
      text: 'LY Reg Wages',
      renderer: function(val, meta) {
          return '$' + Ext.util.Format.number(val, '0,000');
      },
      summaryRenderer: function(val, params, data) {
          return '$' + Ext.util.Format.number(val, '0,000');
      },
      summaryType: 'sum'      
  }, {
      xtype: 'numbercolumn',
      dataIndex: 'thisYearWages',
      text: 'TY Reg Wages',
      renderer: function(val, meta) {
          return '$' + Ext.util.Format.number(val, '0,000');
      },
      summaryRenderer: function(val, params, data) {
          return '$' + Ext.util.Format.number(val, '0,000');
      },
      summaryType: 'sum'                
  }, {
      xtype: 'numbercolumn',
      dataIndex: 'pctChg',
      text: '%Chg',
      renderer: function(val, meta) {
          meta.style = val &lt; 0 ? "color: #FF0000;" : "color: #000000;";
          return Ext.util.Format.number(val, '0,000.00');
      },
      summaryRenderer: function(val, params, data) {
          ???
      },
      summaryType: ??   
      .
      .
      .             
  </code></pre>
  
  <p>So really what I want is the third column to display the result of:
    (SumOfThisYearWages - SumOfLastYearWages) / SumOfLastYearWages</p>
  
  <p>Can this be done? If so, how can I achieve it? </p>
  
  <p>Thanks, in advance, for any feedback!</p>