Now you can view the trendline of a metric in the performance dashboard which reveals the overall direction of the metric - whether it is trending up or down.
To view the Trendline of a performance metric, select the metric in the second dropdown under the Performance Trend View. 
Trendline can also be viewed under individual campaign-level performance.
Once you select the campaign performance, select the metric in the second dropdown to view its trendline. If the metric supports planned values, then the dotted lines show the planned values instead of the trendline. This will be indicated in the chart legend.
[Planned value]
[Metric trendline]
To know more about the performance metrics on the dashboard, click here