There are two character sets included with PLplot. These are known as the standard and extended character sets respectively. The standard character set is a subset of the extended set. It contains 177 characters including the ascii characters in a normal style font, the Greek alphabet and several plotter symbols. The extended character set contains almost 1000 characters, including four font styles, and several math, musical and plotter symbols.
      The standard character set is loaded into memory automatically when
      plstar or plstart is called.  The extended character set is
      loaded by calling plfontld.  The extended character set requires
      about 50 KBytes of memory, versus about 5 KBytes for the standard
      set.  plfontld can be used to switch between the extended and
      standard sets (one set is unloaded before the next is loaded).
      plfontld can be called before plstar.
    
      When the extended character set is loaded there are four different
      font styles to choose from.  In this case, the routine plfont sets
      up the default font for all character strings.  It may be overridden
      for any portion of a string by using an escape sequence within the
      text, as described below.  This routine has no effect when the
      standard font set is loaded.  The default font (1) is simple and
      fastest to draw; the others are useful for presentation plots on a
      high-resolution device.
    
The font codes are interpreted as follows:
font = 1: normal simple font
font = 2: roman font
font = 3: italic font
font = 4: script font
      The routine plschr is used to set up the size of subsequent
      characters drawn.  The actual height of a character is the product of
      the default character size and a scaling factor.  If no call is made
      to plschr, the default character size is set up depending on the
      number of subpages defined in the call to plstar or plstart, and
      the scale is set to 1.0.  Under normal circumstances, it is
      recommended that the user does not alter the default height, but
      simply use the scale parameter.  This can be done by calling plschr
      with def = 0.0 and scale set to
      the desired multiple of the default height.  If the default height is
      to be changed, def is set to the new default
      height in millimeters, and the new character height is again set to
      def multiplied by scale.
    
      The routine plssym sets up the size of all subsequent symbols drawn
      by calls to plpoin and plsym.  It operates analogously to
      plschr as described above.
    
      The lengths of major and minor ticks on the axes are set up by the
      routines plsmaj and plsmin.