\begin{table}%t3
\caption{\label{table3}Differential rotation parameters $A$ and $B$ from Eq.~(1) and their standard errors~$M$ in deg~day$^{-1}$ obtained applying the automatic method to monthly data sets for the year~1998.}
%\centering
\par
\begin{tabular}{rrrrrr}
\hline \hline \noalign{\smallskip}
Month & $N_{\rm s/m}$ & $N_{\rm t/m}$ & $N_{\rm s/t}$ & $A \pm M_A$      & $B \pm M_B$     \\
\hline
6     &   290         &      38       &     7.6       & $14.64 \pm 0.07$ & $-3.89 \pm 0.30$ \\
6st   &   143         &               &               & $14.78 \pm 0.10$ & $-4.44 \pm 0.43$ \\
11    &   211         &      28       &     7.5       & $14.46 \pm 0.08$ & $-3.14 \pm 0.35$ \\
11st  &    90         &               &               & $14.25 \pm 0.12$ & $-2.77 \pm 0.73$ \\
12    &   372         &      58       &     6.4       & $14.53 \pm 0.06$ & $-3.03 \pm 0.20$ \\
12st  &   202         &               &               & $14.60 \pm 0.07$ & $-2.99 \pm 0.28$ \\
\hline
\end{tabular}
\tablefoot {$N_{\rm s/m}$ = the number of structures found per month; 
$N_{\rm t/m}$~= the number of triplets used per month;
$N_{\rm s/t}$~= the average number of structures per triplet.\\
The results after applying the two-step velocity filter are given. The number of structures found in this year, $N_{\rm s/y} = 873$. The index~``st'' after the calender month indicates the subset of selected stable structures.}
\end{table}