The Campaign Trends tab is where you can compare the performance of your campaigns over time. The number on the vertical axis of the graph shows the percentage opened, unopened, unsubscribed, or bounced depending on the selection you make next to Email Category. You can also compare specific Campaign Categories by selecting one from the drop down on the top left of the graph. The horizontal axis of the graph represents the campaign and the Legend will explain which number the point on the axis corresponds to. Number 1 is the most recent campaign sent. The example below shows that the open rate (percentage of emails that were successfully opened) has increased over time.