\begin{table}%t1
\caption{\label{table_data}Dataset specifications.}
%\centerline
 {\small \begin{tabular}{c c c c c c} 
\hline\hline\noalign{\smallskip}
Date & NOAA & $\left \langle \mu \right \rangle$ & $(\mu_{\rm min}, \mu_{\rm max})$ & FOV$_{\rm eff}$ [arcsec$^2$] & Number of pairs \\
\hline
   07-Sept-2004 & 0669 & $0.97 \pm 0.003$ & (0.963, 0.977) & 2034 & 1 \\
   07-Sept-2004 & 0671 & $0.78 \pm 0.008$ & (0.75, 0.8) & 2135 & 1 \\
%\hline
 08-Sept-2004 & 0670 & $0.97 \pm 0.003$ & (0.963, 0.976) & 1906 & 1 \\
 08-Sept-2004 & 0667  & $0.937 \pm 0.003$ & (0.928, 0.945) & 1027 & 2 \\
   08-Sept-2004 & -- & $0.9 \pm 0.005$ & (0.882, 0.916) & 2400 & 1 \\
   08-Sept-2004 & 0671 & $0.63 \pm 0.01$ & (0.58, 0.67) & 1923 & 3 \\
   08-Sept-2004 & 0671 & $0.6 \pm 0.01$ & (0.55, 0.64) & 1763 & 2 \\
   08-Sept-2004 & 0671 & $0.56 \pm 0.01$ & (0.51, 0.6) & 1904 & 1 \\
%\hline
   13-Aug-2006 & 0671 & $0.77 \pm 0.008$ & (0.763, 0.776) & 566 & 1 \\
\hline
\end{tabular}}
\medskip
$(\mu_{\rm min}, \mu_{\rm max})$ indicates the $\mu$ coverage of the images, after their rotation along the disk radius vector pointing towards the closest limb. FOV$_{\rm eff}$ is the effective field of view once the spots and pores have been masked out. The number of image pairs selected for processing and analysis are given in the last column.
\end{table}