\begin{Schunk}
\begin{Sinput}
 (pu <- par("usr"))
\end{Sinput}
\begin{Soutput}
[1] 13.72 21.28  4.16 26.84
\end{Soutput}
\begin{Sinput}
 text(pu[1], pu[4], label = paste("TL"), cex = 3)
 text(pu[2], pu[3], label = paste("BR"), cex = 3)
\end{Sinput}
\end{Schunk}
