\begin{table}%t2
\caption{\label{tan}Tangential directions from observations \citep[][]{bro92,eg99} and the best fitting models.}
%\centering
\small
\begin{tabular}{ccccccc}
\hline
\hline
Model & Scutum & Sagittarius & Carina & Crux & Norma & 3-kpc \\
 & $(^{\circ})$ & $(^{\circ})$ & $(^{\circ})$ & $(^{\circ})$& $(^{\circ})$ & $(^{\circ})$ \\
\hline
observed mean value& 25, 31 & 51 & 284 & 310 & 327 & 339  \\[1mm]
\hline
&&&&&& \\[-8pt]
\multicolumn{6}{l}{For distribution of tracers with $R_{0}=8.5$~kpc and $\Theta_{0}=220$~km s$^{-1}$} \\
2-arm model & 33 & 49 &  &301 & 319 & 330 \\
3-arm model & 26, 36& 58 & 284 & 313 & 325 &   \\
4-arm model &25, 36 & 55 & 283 & 311 & 323 &  \\
polynomial model&27, 33  &53  &284  & 309 & 329 &  \\
\hline
&&&&&& \\[-8pt]
\multicolumn{6}{l}{For distribution of tracers with $R_{0}=8.0$~kpc and $\Theta_{0}=220$~km s$^{-1}$} \\
2-arm model & 33 & 49 &  &303 & 320 & 330 \\
3-arm model & 26, 38& 59 & 282 & 311 & 324 &   \\
4-arm model &26, 37 & 55 & 284 & 310 & 322 &  \\
polynomial model&27, 34  &53  &284  & 309 & 329 &  \\
\hline
&&&&&& \\[-8pt]
\multicolumn{6}{l}{For distribution of tracers with $R_{0}=8.4$~kpc and $\Theta_{0}=254$~km s$^{-1}$} \\
polynomial model&27, 33  &53  &284  & 309 & 329 &  \\
\hline
\end{tabular}
\end{table}