title: Google Charts Diff Chart with custom toolip
body: <p>I have to draw diff pie chart and show custom tooltip text instead of default Old and Current values. Here is the code I use. What should I change to show "my tooltip" and "my another tooltip" instead of default tootip texts?</p>
  
  <pre><code>var d = new google.visualization.DataTable({"cols": [
  {"type": "string" ,"id": "Title"   ,"label": "Title" }, 
  {"type": "number" ,"id": "Count" ,"label": "Count", "p": {"role" : "old-data"} },
  {"type": "number" ,"id": "Count" ,"label": "Count", "p": {"role" : "data"} }, 
  {"type": "string" ,"id": "Tooltip" ,"label": "Tooltip" , "p": {"role" : "tooltip"}}], 
  "rows" : [
  {"c" : [{"v": "Item1"}, {"v": 0}, {"v": 28}, {"v": "my tooltip"}]}, 
  {"c" : [{"v": "Item2"}, {"v": 80}, {"v": 0}, {"v": "my another tooltip"}]}]});
  
  var options = { pieSliceText: 'none', diff: { innerCircle: { radiusFactor: 0.3 } },    sliceVisibilityThreshold: 0, pieSliceText: 'label'};
  
  var chartDiff = new google.visualization.PieChart(document.getElementById('piechart_diff'));
  chartDiff.draw(d, options);
  </code></pre>