This sets up the size of all subsequent symbols drawn by plpoin and
      plsym.  The actual height of a symbol is the product of the default
      symbol size and a scaling factor as for the character height.
    
- 
          def(PLFLT
- 
            The default height of a symbol in millimeters, should be set to
            zero if the default height is to remain unchanged.
           
- 
          scale(PLFLT
- 
            Scale factor to be applied to default to get actual symbol
            height.
           
      Redacted form: plssym(def, scale)
    
      This function is used in example 29.