/n 11 def
/scale 25 def
/fs 12 def

20 650 translate

/Helvetica findfont
fs scalefont setfont

1 1 n {
    /x exch def
    /ns 30 string def
    x ns cvs
    x scale mul dup 0 moveto ns show
    neg 0 exch moveto ns show
    1 1 x {
        /y exch def
        /nv 30 string def
        x y mul nv cvs pop
        x scale mul y neg scale mul moveto nv show
    } for
} for

0 scale 2 div neg fs 2 div add moveto
scale n 1 add mul scale 2 div neg fs 2 div add lineto
scale 2 div fs 2 div add fs moveto
scale 2 div fs 2 div add scale n 1 add mul neg fs add lineto
stroke

showpage