15.64.52  SIZE 

This sets the physical size of the plot.  Once set it remains the same
until a new SET SIZE command is issued.  This command should only be used
immediately after a NEW PLOT command or a SET DEVICE command.  It may not
be used after any commands that plot data.
SET SIZE [[X=]x [BY|Y=] y]
     [UNITS=units] [CM|CENTIMETERS|MM|MILLIMTERS|METERS|INCHES]
     [MAGNIFY|REDUCE=factor]
     [SIDEWAYS|ROTATED|NORMAL|ORIENTATION=n]
     [MARGINS=[nl,[nr,[nb,[nt]]]]] [LEFT=n] [RIGHT=n] [BOTTOM=n] [TOP=n]
If no options are specified the sizes are reset to the defaults.
(Default:NORMAL 13 by 10 inches MARGINS=0)