code: public T customMetric(int index, String value) {
      customMetrics.put("cm" + index, value);
      return (T) this;
    }
docs: <div class="ind">
  <p>
  Optional.
  </p>
  <p>Each custom metric has an associated index. There is a maximum of 20 custom metrics (200 for Premium accounts). The name suffix must be a positive integer between 1 and 200, inclusive.</p>
  <table border="1">
  <tbody>
  <tr>
  <th>Parameter</th>
  <th>Value Type</th>
  <th>Default Value</th>
  <th>Max Length</th>
  <th>Supported Hit Types</th>
  </tr>
  <tr>
  <td><code>cm[1-9][0-9]*</code></td>
  <td>integer</td>
  <td><span class="none">None</span>
  </td>
  <td><span class="none">None</span>
  </td>
  <td>all</td>
  </tr>
  </tbody>
  </table>
  <div>
  Example value: <code>47</code><br>
  Example usage: <code>cm[1-9][0-9]*=47</code>
  </div>
  </div>