\begin{table}%t2
\caption{\label{calib}Calibration summary.}
%
\par
%\centerline
 $$
\begin{tabular}{lllllr@{ (}ll}
\hline \hline
Run  &  Telescope & Retarder        & $\tau$ ($^\circ$)      &    Zero ($^\circ$)       & \multicolumn{2}{c}{Efficiency (\%)}   &  PA$_{\rm corr}$ ($^\circ$) \\
\hline 
2003 Sep. &  0.6~m & $\lambda$/2$-$800~nm  &    141   &    35          &  100.1 & 0.2)$^{a}$  &  $+$138.0   \\
%%2004 May &  1.6~m & $\lambda$/2$-$800nm  &    141   &    35          &   98.4 & 2.7)        &  $+$59.3    \\
2005 Jun. &  1.6~m & $\lambda$/4$-$NIR    &    87    &    47          &   99.4 & 0.4)$^{b}$  &  $+$51.2    \\
2005 Oct. &  0.6~m & $\lambda$/4$-$NIR    &    87    &    47          &   99.4 & 1.3)        &  $+$41.9    \\
\hline
\end{tabular}$$
\medskip
Errors in parenthesis.\\
$^a$ Mean of three measurements.\\
$^b$ Mean of two measurements. 
\end{table}