just got a brand-new LG L226 WTQ and it refused to align the picture properly, the auto set feature left a full of 15cm on the left unused and black, and same 15cm on the right hidden. Changing position of the picture manually (by drive down the “HORIZONTAL” value to zero) reduced the black/hidden space to about 15mm, but did not close the gap.
So, some modeline writing is necessary – but since I am no masochist, I preferred the use of “xvidtune” – it’s a nice tool that I did not know so far. If a DISPLAY variable is set, you are able to adjust your xorg modeline values verbosely and well-explained. Quick-check with “apply”, quit the tool and re-run it as “xvidtune -show” to get the new and fitting ModeLine. Become root, edit your “Monitor” and “Modes” section in xorg.conf – make it look like that: