anchor.diff:        fill_width = 2
         cont_color = 0
         cont_width = 0
  -      call plshades(z, defined, -1._plflt, 1._plflt, -1._plflt, &
  -        1._plflt, &
  -        shedge, fill_width, &
  -        cont_color, cont_width, xg2, yg2 )
  -
  -      call plcol0(1)
  -      call plbox('bcnst', 0.0_plflt, 0, 'bcnstv', 0.0_plflt, 0)
  -      call plcol0(2)
  -      call plcont(w, clevel, xg2, yg2)
  +      call plshades(z(:NX,:NY), defined, -1._plflt, 1._plflt, -1._plflt, &
  +        1._plflt, &
  +        shedge, fill_width, &
  +        cont_color, cont_width, xg2(:NX,:NY), yg2(:NX,:NY) )
  +
  +      call plcol0(1)
  +      call plbox('bcnst', 0.0_plflt, 0, 'bcnstv', 0.0_plflt, 0)
  +      call plcol0(2)
  +      call plcont(w, 1, nx, 1, ny, clevel, xg2, yg2)
         call pllab('distance', 'altitude', &
           'Bogon density, with streamlines')
   
  
positive.code:       fill_width = 2
        cont_color = 0
        cont_width = 0
        call plshades(z, defined, -1._plflt, 1._plflt, -1._plflt, &
          1._plflt, &
          shedge, fill_width, &
          cont_color, cont_width, xg1, yg1 )
  
        call plcol0(1)
        call plbox('bcnst', 0.0_plflt, 0, 'bcnstv', 0.0_plflt, 0)
  
negative.code:       fill_width = 2
        cont_color = 0
        cont_width = 0
        call plshades(z(:NX,:NY), defined, -1._plflt, 1._plflt, -1._plflt, &
          1._plflt, &
          shedge, fill_width, &
          cont_color, cont_width )
  