\begin{table}%T2
\par
\caption{\label{levelcodes}Definition of the method of measurement of 21-cm line width.
The columns are arranged as follows:
Col.~1:~number of published 21-cm line widths;
Col.~2:~code number of the method in LEDA; 
Col.~3:~description of the method.}
%\centering
\par
\begin{tabular}{rrl}
\hline\hline
$n$ & code   &Definition of the level    \\
\hline
20~684 & 5  & 50\% of the maximum   \\
17~546 & 1  & 20\% of the maximum   \\
4702  & 8  & 50\% of the mean      \\
3067  &10  & $2V_{\rm M}^{\sin i}$ from rotation curve  \\
1503  & 4  & 40\% of the maximum   \\
1268  & 2  & 25\% of the maximum   \\
1069  & 6  & 20\% of the mean      \\
731   & 9  & mean of codes 1 and 8 \\
395   & 7  & 25\% of the mean      \\
139   & 0  & undetermined   \\
\hline
51~113 &    & total          \\
\hline
\end{tabular}
\end{table}