\begin{table}%t6
\caption{\label{table6}Some [Fe/H] determinations of  the globular cluster M 92
measured by different authors in different epochs.} 
\small%\centering
\par
\begin{tabular}{lll}
 \hline \hline 
 Reference &[Fe/H]$_{\rm dex}$&error$_{\rm dex}$ \\
  \hline
Wallerstein \& Helfer (\cite{Wallerstein1966}) &$-2.1$ &   \\  
Harris \& Racine (\cite{Harris1979}) &$ -2.12$ &$\pm$$0.2$ \\  
Zinn (\cite{Zinn1980a}) &$ -2.19$ &$\pm$$0.1$      \\ 
Zinn \& West (\cite{Zinn1984}) &$ -2.24$&$\pm$$0.08$  \\ 
Harris (\cite{Harris1996})&$-2.28$&  \\ 
Gratton et~al. (\cite{Gratton1997})&$ -2.16$&$\pm$$0.07$ \\  
Smriglio et~al. (this paper)&$-2.11$&$\pm$$0.14$ \\ \hline
\end{tabular}
\end{table}