Preview of screen on second monitor I  want to be able to see a preview of what is being shown on the second monitor attached via VGA on the Macbooks screen. In other words I want to monitor what is being shown without having to look at the other screen (it is not facing me).

Surely presenters want to know what the audience is seeing?
Using various software with a secondary display, you can enter "presenter mode" and this allows you to see the current and next slide, with notes that only the presenter can view.

This is available in Microsoft Powerpoint and Apple Keynotes. With Powerpoint, you can enter 'presenter mode' using Option-Return [⌥↩︎]:



With Keynote, you can customise presenter notes and enter presenter mode using the menu option: Play > Customise Presenter Notes.

I can't test as its the weekend but if I was at work, I could connect to a display and verify that it enters (as I believe) presenter mode automatically