The Overlay tool allows you to place, or overlay, a separate page from your plans onto the page that you are currently viewing.
...
To turn the overlay on or off, simply click the light bulb icon next to its name.
See video below on Here's a video that shows how to use the Standard Overlay tool:
Widget Connector width 640 url https://www.youtube.com/watch?v=6hZBkMHja6Q height 360
And here's one for Comparative Overlay:
Widget Connector width 640 url https://www.youtube.com/watch?v=XurRE_EarH0 height 360