// Use CVT to generate standard X config line
cvt -v 1366 768 60
# 1368x768 59.88 Hz (CVT) hsync: 47.79 kHz; pclk: 85.25 MHz
Modeline "1368x768_60.00"   85.25  1368 1440 1576 1784  768 771 781 798 -hsync +vsync

// use xrandr
sudo xrandr --newmode "1368x768_60.00"   85.25  1368 1440 1576 1784  768 771 781 798 -hsync +vsync

// identify the correct "screen" identifier
xrandr | grep -e " connected [^(]" | sed -e "s/\([A-Z0-9]\+\) connected.*/\1/"
LVDS-1
VGA-1

// add the newly created resolution
sudo xrandr --addmode VGA-1 1368x768_60.00