\begin{table} %t2
\caption{\label{tab2}Photometric completeness $f$ and the associated
$1~\sigma$~uncertainty, both in percent, in the four regions in which 
we have divided our NGC~6218 field.} 
%\centering
\par
\begin{tabular}{ccccccccc}
\hline \hline 
  &  \multicolumn{2}{c}{\em Centre} & \multicolumn{2}{c}{\em Ring 1}& 
     \multicolumn{2}{c}{\em Ring 2} & \multicolumn{2}{c}{\em Ring 3}\\ 
{\em $ V $} & 
  $f$ & $\sigma$ & $f$ & $\sigma$ & $f$ & $\sigma$ & $f$ & $\sigma$ \\
\hline
 18.25 & 91 & 2 & 94 & 1 & 95 & 2 & 96 & 1 \\
 18.75 & 86 & 3 & 93 & 2 & 94 & 2 & 96 & 1 \\
 19.25 & 79 & 6 & 92 & 4 & 93 & 2 & 95 & 1 \\
 19.75 & 76 & 5 & 90 & 2 & 91 & 1 & 94 & 1 \\
 20.25 & 75 & 4 & 86 & 4 & 89 & 1 & 92 & 1 \\
 20.75 & 67 & 7 & 82 & 2 & 86 & 2 & 90 & 1 \\
 21.25 & 59 & 9 & 77 & 2 & 83 & 2 & 88 & 2 \\
 21.75 & 47 & 6 & 70 & 2 & 80 & 2 & 84 & 2 \\
 22.25 & 34 & 5 & 62 & 5 & 74 & 2 & 80 & 2 \\
 22.75 & 22 & 4 & 48 & 4 & 63 & 2 & 72 & 1 \\
 23.25 & 13 & 4 & 31 & 3 & 49 & 3 & 59 & 2 \\
 23.75 &  6 & 3 & 18 & 3 & 33 & 2 & 42 & 2 \\
 24.25 &  2 & 1 &  7 & 3 & 19 & 4 & 23 & 2 \\ 
\hline
\end{tabular}
\end{table}