Setting a non detected resolution on modern xrandr system
This script distills the knowledge needed to get my old samsung syncmaster 213T to work at native res from my macbook air running gnome 3.
# if you are adapting this script get the modeline information by running cvt
# then to the below to add this named mode with its config details to the xrandr system
xrandr --newmode "Syncmaster1600" 161.00 1600 1712 1880 2160 1200 1203 1207 1245 -hsync +vsync
# make the new mode setable on this monitor
xrandr --addmode VGA1 Syncmaster1600
# now the new mode should be in the display control panel, but we will go ahead and set it here.
# sets the vga out to use the modes from above
xrandr --output VGA1 --mode Syncmaster1600