subroutine plots
*                =====
*     PostScript header
*     -----------------
      write(7,'(a)') '%!'
      write(7,'(a)') '/u {stroke newpath moveto} def /d {rlineto} def'
      write(7,'(a)') '72 72 scale % unit is 1 inch'
      write(7,'(a)') '90 rotate % Landscape mode'
      write(7,'(a)') '0. -210.0 25.4 div translate'
      write(7,'(a)') '1. 2400. div 1. 2400. div scale'
      write(7,'(a)') '2400. 25.4 div 0.1 mul setlinewidth % 0.1 mm'
      write(7,'(a)') 'newpath'
      return
      end