  plsmaj(def, scale)
  ******************

  plsmaj

  This sets up the length of the major ticks. The actual length is the
  product of the default length and a scaling factor as for character height.

  def (PLFLT, input): The default length of a major tick in millimeters,
  should be set to zero if the default length is to remain unchanged.

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

