title: Putting the Z-Coordinate in the Highcharts Tooltip
body: <p>I have three graphs. All three graphs have the same x axis values (category), different y-values, and the same z-value (date). The graphs have synced tooltips when you hover over a point. I want to be able to populate the tooltip with the z-coordinate for each point. I <strong>do not</strong> want to plot the z coordinate... just have it show in the tooltip. I am not sure how to do this because there are more multiple graphs with synced tooltips.</p>
  
  <p>I made a basic example to show how to put the z-value (date) in a tooltip for one graph. <a href="https://codepen.io/austeng/pen/ZEGxWyK" rel="nofollow noreferrer">https://codepen.io/austeng/pen/ZEGxWyK</a></p>
  
  <pre><code>Highcharts.chart('container', {
      tooltip: {
        formatter: function() {
          return 'x: ' + this.x + ', y: ' + this.y + ', z: ' + Highcharts.dateFormat('%b/%e/%Y',
            new Date(this.point.z));
        }
      },
    xAxis:{
      type: 'category'
    },
      series: [{
        data: [{
            x: 0,
            y: 0,
            z: 1564358400000
          },
          {
            x: 1,
            y: 5,
            z: 1564531200000
          },
          {
            x: 2,
            y: 2,
            z: 1564963200000
          }
        ]
      }]
    });
  </code></pre>
  
  <p>This is my codepen for the three graphs: <a href="https://codepen.io/austeng/pen/gOppRWY" rel="nofollow noreferrer">https://codepen.io/austeng/pen/gOppRWY</a></p>
  
  <p>Any help on how to extend my example for one graph to my current code of three graphs w/sync tooltip would be very appreciated. Thanks.</p>