title: Multiple baselines with dual y-axis Google Chart
body: <p>I'm using the Google Visualization API for a simple sales chart that has two series, number of sales and sales value, that I'm showing on a column chart with two vetical axes.  The sales value can be negative, such as for returns, but this is causing the graph to show two different baselines.  The zero baseline for number of sales is in line with the lowest sales value figure.  Here's an example of the code with some sample data:</p>
  
  <pre><code>google.load('visualization', '1.0', { 'packages': ['corechart'] });
  google.setOnLoadCallback(drawSalesChart);
  
  function drawSalesChart() {
      var dataTable = new google.visualization.DataTable();
      dataTable.addColumn('string', 'Order Source');
      dataTable.addColumn('number', 'Num Sales');
      dataTable.addColumn('number', 'Sales Value');
  
      dataTable.addRows([
          ['Web (Order)', 300, 31000],
          ['Call Centre (Order)', 700, 61000],
          ['Call Centre (Return)', 50, -4100],
          ['Call Centre (Exchange)', 10, 800]
      ]);
  
      var options = {
          title: 'Sales by Order Source',
          hAxis: { title: 'Order Source' },
          series: {
              0: { targetAxisIndex: 0 },
              1: { targetAxisIndex: 1 },
          },
          vAxes: {
              0: { title: 'Num Sales' },
              1: { title: 'Sales Value' }
          }
      };
  
      new google.visualization.ColumnChart(
          document.getElementById('livesales-chart-container')).draw(dataTable, options);
  }
  </code></pre>
  
  <p>I've been through the API documentation as there's information on setting the baseline but there doesn't seem to be a way to tie the zero of each vAxis to the same point.  I've tried searching Google and StackOverflow and there are similar questions but I can't see that anyone has had this problem.</p>
  
  <p>How can I, or even can I, show a single baseline at zero for both series?</p>