  plssym(def, scale)
  ******************

  plssym

  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, input): The default height of a symbol in millimeters,
  should be set to zero if the default height is to remain unchanged.

  scale (PLFLT, input): Scale factor to be applied to default to get
  actual symbol height.

