Viewing a part of the screen in a window on Linux

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http://askubuntu.com – I plan to make a presentation with a live demo using my wide screen Ubuntu 12.10 Laptop and a projector. My plan is to connect the projector as a second (small) display and put my slides and live-demo there. It would be convenient, if I could see the projector display on my laptop LCD screen within a window (no zoom or stretch needed). So my question is: How can I see selected part of a screen within a window? Thank you for your suggestions! PS Other possibilities are typing on laptop and looking on the projector screen and not at the audience Cloning laptop display to the projector displ (HowTos)