\begin{table}%t4
\caption{Mean plate scale and detector orientation for our different observing 
runs. The orientation angle gives the position of true North east of the 
vertical.            \label{table4}      }
%\centering
\par
\begin{tabular}{c c c c}     % 7 columns 
\hline\hline       
Epoch     & Camera & Plate scale        & Orientation \\
          &        & (mas pixel$^{-1}$)& (deg)       \\
\hline
2002 Dec. & S13    & $13.16\pm0.03$    & $0.15\pm0.11$  \\
2002 Dec. & S27    & $26.92\pm0.10$    & $0.14\pm0.10$  \\ 
2003 May  & S13    & $13.16\pm0.06$    & $0.23\pm0.17$ \\
2004 Jun. & S13    & $13.18\pm0.06$    & $-0.06\pm0.17$  \\
2004 Jun. & S27    & $26.91\pm0.14$    & $0.29\pm0.23$  \\
2004 Nov. & S13    & $13.19\pm0.06$    & $0.10\pm0.16$  \\
2004 Nov. & S27    & $26.89\pm0.14$    & $0.29\pm0.16$  \\                            
2005 May  & S13    & $13.17\pm0.06$    & $0.06\pm0.15$  \\ 	        
2005 May  & S27    & $26.88\pm0.13$    & $0.31\pm0.15$   \\  
2005 Dec. & S13    & $13.16\pm0.08$    & $0.20\pm0.17$  \\ 	        
2005 Dec. & S27    & $26.99\pm0.11$    & $0.26\pm0.12$   \\ 	 
\hline                  
\end{tabular}
\end{table}