\begin{table}%t2
\caption{Number of stars observed ($N$) and mean internal errors~($\sigma$) as a~function of apparent visual magnitude.}\label{error67}
%\centering
\small
\begin{tabular}{ccccccccccc}
\hline \hline
\multicolumn{1}{c}{$V$ range} & 
\multicolumn{2}{c}{$V$} & 
\multicolumn{2}{c}{$(b-y)$} & 
\multicolumn{2}{c}{$m_1$} & 
\multicolumn{2}{c}{$c_1$} & 
\multicolumn{2}{c}{H$_{\beta}$} \\
&&&&&&&&&& \\[-8pt]
\hline
& $N$&$\sigma$ & $N$&$\sigma$ & $N$&$\sigma$ & $N$&$\sigma$ &$N$&$\sigma$ \\
\hline
8--9 &    3 & 0.029 &    3 & 0.028 &    3 & 0.029 &    2 & 0.004 &      &        \\
9--10 &    8 & 0.008 &    7 & 0.007 &    6 & 0.008 &    7 & 0.007 &    2 & 0.001  \\
10--11 &   22 & 0.003 &   22 & 0.002 &   22 & 0.003 &   22 & 0.005 &   10 & 0.009  \\
11--12 &   28 & 0.004 &   28 & 0.022 &   26 & 0.003 &   26 & 0.005 &   14 & 0.016  \\
12--13 &  114 & 0.004 &  114 & 0.003 &  114 & 0.004 &  114 & 0.005 &   56 & 0.009  \\
13--14 &  199 & 0.003 &  199 & 0.003 &  198 & 0.004 &  197 & 0.006 &   75 & 0.015  \\
14--15 &  240 & 0.020 &  239 & 0.005 &  238 & 0.006 &  237 & 0.009 &   63 & 0.016  \\
15--16 &  277 & 0.007 &  277 & 0.010 &  275 & 0.011 &  269 & 0.018 &   57 & 0.019  \\
16--17 &  299 & 0.011 &  299 & 0.015 &  272 & 0.021 &  233 & 0.031 &   10 & 0.016  \\
17--18 &  307 & 0.021 &  306 & 0.029 &  245 & 0.041 &  109 & 0.043 &    1 & 0.033  \\
18--19 &  259 & 0.040 &  259 & 0.058 &  130 & 0.073 &   46 & 0.059 &      &        \\
19--20 &   75 & 0.093 &   75 & 0.125 &   18 & 0.141 &   12 & 0.106 &      &        \\
\hline
Total & 1831 &       & 1828 &       & 1547 &       & 1274 &       &  288 &        \\
\hline
\end{tabular}
\end{table}