You can specify virtually any screen coordinate system that is appropriate for the objects that you are defining. Typically, the screen size should equal the resolution of the workstation's graphics board, which you can access by specifying the following:

 

screen size device units

 

Once you have defined a screen size, you can run the ESL program on any graphics board or resolution, and the screen coordinate system will get mapped to the actual resolution of the new display. You do not need to change the defined screen size. For example, if a program is written on a workstation using a VGA monitor and you define a resolution of 640 480, and run the program on a workstation using a completely different graphics board or resolution, all objects will be mapped proportionally to the new resolution, even without specifying a new screen size.

 

The only advantage to defining a different screen size than the current one is if the current resolution has very poor proportions. A monitor is usually one-third wider than it is high. If you preserve these proportions when you define new screens, you can preserve the proportions of circles, arcs, and ellipses. However, if you define a screen such as the following:

 

screen size 100 300

 

and display a circle on that screen, the circle is not displayed as exactly round, because this screen's proportions are not 4:3.