For example the external monitor is identified as VGA-1
Invoke the external monitor
$ xrandr --output VGA-1 --auto
$ xrandr --output VGA-1 --auto
Place the external monitor on the right-hand-side (of my laptop being LVDS-1)
$ xrandr --output VGA-1 --right-of LVDS-1
$ xrandr --output VGA-1 --right-of LVDS-1
Rotate the VGA-1 display (counter clockwise)
$ xrandr --output VGA-1 --right-of LVDS-1 --rotate left
$ xrandr --output VGA-1 --right-of LVDS-1 --rotate left