If ssh is NOT being used the xdisplay procedure is available on all Starlink machine to wrap up what
you need to type to get X output from the machine that you are logged into back to your
X server.
To get X output drawn on your X server from a remote client, just type xdisplay before running the
program. If you type xdisplay when you are not logged into a remote system, then nothing will
happen and the output will still appear on your screen.
What XDISPLAY does is to see where you logged in from and executes an appropriate command to point the X output back to you.