To choose which cursor to use, see the menu commands under Graphs / Options / Cursor Type within a Graph window.
When using either the Track Ball or Crosshair cursor type the cursor will highlight the actual values on the graph's lines. The value of the position closest to the cursor will be displayed in the status bar, and this location will be highlighted with either a small Track Ball or a large Crosshair. When the cursor is off, no highlighting occurs, and the value directly beneath the cursor is displayed in the status bar.
Tip: Use the keyboard shortcut 'F3' to scroll between the different cursor types.