Listing 3. Histo-y and Histo-z Subroutines

/Histo-y {
  30 mul 100 add /y exch def
  1993 sub 50 mul 150 add /x exch def
  0.9 setgray newpath
  x 100 moveto x y lineto x 20 sub y lineto x 20 
	sub 100 lineto
  closepath fill
  0 setgray newpath
  x 100 moveto x y lineto x 20 sub y lineto x 20 
	sub 100 lineto
  closepath stroke
} def

/Histo-z {
  30 mul 100 add /y exch def
  1993 sub 50 mul 150 add /x exch def
  0.1 setgray newpath
  x 100 moveto x y lineto x 20 add y lineto x 20 
	add 100 lineto
  closepath fill
  0 setgray newpath
  x 100 moveto x y lineto x 20 add y lineto x 20 
	add 100 lineto
  closepath stroke
} def