15.64.12  CLEAR 

SET {CLEAR|ERASE} {DEFERRED|IMMEDIATE}

     1.  DEFERRED  -  After  a CLEAR or NEW PLOT command the screen is not
         cleared until data is plotted.  In other words the  current  plot
         remains on the screen until the new plot appears.
     2.  IMMEDIATE  -  The  screen is cleared immediately after a CLEAR or
         NEW PLOT command.