Whenever you click the graph, a vertical line appears at the point where you clicked and the Timestamp, Value, and Screen Relative Time columns in the Legend update. The vertical line marks the time at that point. Generally, you click the graph to select a data point or an event, or to read the timestamp for a particular point on the graph. You can move the time line between data points, events, and areas of the graph. As you move a time line, the Timestamp, Value, and Screen Relative Time columns in the Legend update.
To remove a time line, click outside the graph on the right or left hand side.