Detailed information about a point in the graph can be displayed by hovering on any of the lines.
As your cursor hovers over the graph, a disk along with "help text" pop up giving information about the data on the x-y coordinate selected at that point.
The color of the disk changes according to the line you are hovering on.
The help text indicates:
The name of the line plotted that your cursor in on Parent topic: Working with Graphs
The date and time at that point
The value at the targeted point