\begin{table}%t1
\caption{Details of the observations of the Crab nebula with \hess\ between October 2003 and January 2005. 
For the purposes of this study, the data has been divided into 3 subsets.}
\label{tab:obs}
%\centering
\small
\begin{tabular}{cccccccccc}
\hline \hline
Data Set&Date    &$N_{{\rm tels}}$& $Z$ range      &$\langle {Z} \rangle$ &Offset  &$N_{{\rm runs}}$ &Obs. Time &Live-time &Mean System rate\\
        &        &                   &(\dg)        &(\dg)          &(\dg)   &                    &(h)   &(h)   &(Hz)\\
\hline                                                                           
I       &10/'03--1/'04 &3           &45--55        &46.6           &0.5--1.5 &12                  &5.3       &4.8       &179\\  
II      & 1/2004        &4           &45--65        &54.4           &0.5--1.5 &14                  &6.3       &5.7       &240\\
III     &10/'04--1/'05 &4           &45--55        &47.9           &0.5--1.5 &26                  &11.3      &10.6      &180\\ 
\hline
Total   &        &                   &45--65        &50.2           &0.5--1.5 &52                  &22.9      &21.1      &196\\
\hline
\end{tabular}
\end{table}