\begin{table}%t2
\caption{\label{tab:lines} The unabsorbed flux in ph ${\rm m^{-2}}~{\rm s^{-1}}$ for the \ion{O}{vii} forbidden emission line for all high resolution spectral observations of NGC 5548. }   
\par
%\centerline
{                         
\begin{tabular}{l c}         
\hline\hline                 
Year (month) & \ion{O}{vii}  \\  
\hline         
1999 (Dec.) & $0.81\pm0.16$ \\
2000 (Feb.) & $0.82\pm0.18$ \\
2000 (Dec.) & $1.3 \pm0.2 $\\
2001 (Jul.) & $ 1.1\pm0.1 $ \\
2002 (Jan.) & $0.75\pm0.07$ \\     
2005 (Apr.) & $0.35\pm0.06$  \\  
2007 (Aug.) & $0.27\pm0.06$ \\ 
\hline
\end{tabular}}
\medskip
\par
All errors are calculated at a 68\% confidence level.
\end{table}