Monitor and Ubuntu screen resolution don't match

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http://askubuntu.com – Few days ago I manage to have 1366x768 resolution option in my Ubuntu 12.04 (nvidia x driver), but the screen (fiscal) and the option resolution in the system settings under monitor, doesn't match each other, I have chosen 1366x768 as the option, but seems that in the screen its just show 1280x768 this is the image : On the right hand side is nvidia x setting and the left is monitor resolution. Should both be on the same setting or doesn't it matter? Should I only focus on the setting that is reflecting in Ubuntu 12.04 by the system setting monitor? What about the refresh rate, does that (HowTos)