Mirror displays with Ubuntu 14.04

Some years ago I switched from Windows to Ubuntu. Now Ubuntu 14.04 is installed on my Acer TravelMate 5742G with:

• Intel Core i5-460M
• Nvidia GeForce Gt 420M and Nvidia binary driver version 331.38
• 15.6 HD (1366x768)

When I used Windows and had to present something in front of some people I mirrored the display of my laptop and the projector. This was really helpful because in most cases the display of the projector was behind me. Unfortunately, this is not possible with Ubuntu anymore. I tried it with various projectors and displays that worked with Windows before.

In cases the resoultion of both screens did not match Windows cutted my screen and added two black bar to the sides of my laptop display. Is it possible to add this very nice feature to Ubuntu? Maybe I should add that Ubuntu offers only one resolution for my laptop display.

Update 1:

Here is an image of my screen setting (in German, but the buttons are still the same):

To mirror displays in Ubuntu

Open system preferences Click screen displays (under hardware) and then tick the check box mirror displays Then click apply