documentclass{article}
usepackage[pdf]{pstricks}
begin{document}
psset{unit=1mm}

begin{pspicture}(60,25)
  psframe(1,1)(20,20)
end{pspicture}
begin{pspicture}(60,25)
  psframe(1,1)(20,20)
end{pspicture}

end{document}