\begin{table}%T2
%\centering
\par
\caption{Neutral oxygen wavelengths (1s$-$2p transition).
1)~Mc~Laughlin \& Kirby (\cite{Laughlin1998});
2) Krause (\cite{Krause1994});
3) Stolte et~al. (\cite{Stolte1997});
4) Paerels et~al. (\cite{Paerels2001});
5) Nicastro et~al. (\cite{Nicastro2002});
6)~de~Vries et~al. (\cite{Vries2003});
7) Cagnoni et~al. (\cite{Cagnoni2004}).}
\label{calib}
\begin{tabular}{ccc}
\hline\hline
$\lambda$ (\AA)& Method &  Ref.\\
\hline
23.467  & Theoretical & 1  \\
$23.489\pm0.004$  & Experimental & 2 \\
$23.536\pm0.002$  & Experimental & 3 \\
$23.52\pm0.03$  & Chandra, X0614+091 & 4 \\
$\rm 23.509^{+0.008}_{-0.018}$ & Chandra, PKS~2155-304 & 5 \\
$23.50 \pm 0.01$  & XMM & 6 \\
$23.510\pm0.015$ & XMM, PKS~2155-304 & 7 \\
$23.510\pm0.007$ & XMM, Mkn~421 & ToO obs.\\
$23.507\pm0.013$ & XMM, Mkn~421 & Arch. data \\
$23.510\pm0.013$ & XMM, Mkn~421 & Total \\
\hline
\end{tabular}
\end{table}