9. - Graphics Filter Commands

      
•        initializing, opening and closing graphics filters       
•        erasing old plot material from graphics filters       
•        controlling the echoing of commands

9.1. - Commands covered
9.2. - zi initialize graphics filter
9.3. - zf select filter
9.4. - sc select filter scaling factors
9.5. - zO# select filter line style
9.6. - ze erase old plot
9.7. - zE erase current window
9.8. - zq don't write text to screen
9.9. - zw don't close filter yet
9.10. - zx close filter
9.11. - zs close filter, synchronous