I'm trying to launch an application on to a specific display. Yes, I know it's *supposed* to launch onto whatever window I have my mouse, but this doesn't happen.

Doing:
$ DISPLAY=":0.0" gnome-calculator

launches the application fine, but any other numbers besides "0"s there causes an error, eg,

(gnome-calculator:4211): Gtk-WARNING **: cannot open display: :1.0

Any ideas what the syntax is supposed to be for the $DISPLAY variable?

More info:
Nvidia cards, three displays, gnome not unity.

A snippet from xorg.conf that may be relevant:
Section "ServerLayout"
Identifier "Layout0"
Screen 0 "Screen0" 1920 0
Screen 1 "Screen1" 0 0
Screen 2 "Screen2" 3840 0
InputDevice "Keyboard0" "CoreKeyboard"
InputDevice "Mouse0" "CorePointer"
Option "Xinerama" "1"
EndSection


Thanks!