How to add a cursor (cross) that follows a curve?

In Plot->Chart Settings for Active Plot..., click on the Tools tag. Then click on the Add… button. From the list select Cursor and click on the Add button. From the Series: list box, select the curve you wish the cursor to follow. Turn on the Snap and Follow mouse check boxes. Click Close to exit the dialog box.

Note that if you selected the active measurement, the cursor values are displayed at the Status Bar.