\begin{table}%t3
\caption{\label{table:3}Global astrometric solution for WFI CCD mosaics. }
%\centering
\par
\begin{tabular}{c c c c c c}
\hline\hline \noalign{\smallskip}
Sky    & Zero-point        & \multicolumn{2}{c}{(RA, Dec)--UCAC2}  & UCAC2~\\
path   & offset before G.S. & before G.S.  &   after G.S.        &   stars~  \\
       & $\Delta\alpha$cos$\delta$ ~  $\Delta\delta$ ~ &  $\sigma_{\alpha}$  ~ $\sigma_{\delta}$ &  $\sigma_{\alpha}$ $\sigma_{\delta}$ &  \\
 Year  &      mas                                   mas                  &      mas              mas        &   mas               mas     &  \\
\hline
2008   &       $-$13           ~                    $-$04                  &       112             ~    107   &        59     ~    58  &       6001 ~   \\
2009   &       $-$09           ~                    $-$01                  &       112             ~    103   &        58     ~    55  &       4693 ~   \\
2010   &       $-$03           ~                    $-$03                  &       133             ~    126   &        59     ~    57  &      11013 ~   \\
2011   &       $-$08           ~                    $-$03                  &       134             ~    129   &        61     ~    59  &       8988 ~   \\
2012   &       $-$06           ~                    $-$05                  &       139             ~    131   &        62     ~    61  &       7563 ~   \\
2013   &       $-$03           ~                    $-$04                  &       145             ~    141   &        63     ~    62  &       6068 ~   \\
2014   &       $-$06           ~                    $+$02                  &       135             ~    138   &        60     ~    60  &       6439 ~   \\
2015   &       $-$06           ~                    $-$03                  &       100             ~    098   &        57     ~    57  &       7524 ~   \\
\hline
\end{tabular}
\tablefoot {Tangent plane technique results. Zero point position offsets were computed from averaged observed minus UCAC2 star position differences, before applying the global mosaic solution procedure~(G.S.). Due to the tangent plane technique, by definition they are zero after G.S. process. The~($\sigma_{\alpha}$, $\sigma_{\delta}$)s of tangent plane technique solutions refer to observed minus UCAC2~positions computed before and after the G.S.~procedure. The last column is the number of used UCAC2 reference stars (see details in Sect.~4.3).}
\end{table}