\begin{table}%t1
%\centering
\par
\caption{Distribution of clusters according to the number of members~($N_t$) 
used for age determination. Typically, the more stars used, the more
reliable the age determination. Cases $i$ to $iii$ are explained in the~text.\label{NA_tbl}}
\begin{tabular}{rrrrrr}
\hline\hline
$N_t$&   $N$ clusters & $N_t$ &   $N$ clusters& $N_t$ &   $N$ clusters\\
      &              &        &           &        &              \\
\hline
$>$10 &   21        &   6    &   17      &   1    &  189         \\
 10    &    5        &   5    &   14      &  $i$   &   47         \\
  9    &    6        &   4    &   29      & $ii$   &    5         \\
  8    &    7        &   3    &   56      &$iii$   &   25         \\
  7    &    3        &   2    &   96      &        &              \\
\hline
\end{tabular}
\end{table}