\begin{table}%t1
\caption{\label{tab:comparisons_dm}
rms errors of the magnitude differences (instrumental system) between 
the comparison stars in units of 0.1~mmag.
$N$ is the total number of magnitude differences. 
}
\small%\centering
\par
\begin{tabular}{lrrrrr} 
\hline
\hline 
Objects                    &  $N$ & $y$ & $b$ & $v$ & $u$ \\ 
 \hline
 AD~Boo                    &     &     &     &     \\
HD~128369, HD~129430 (C1,~C2) & 196 &  47 &  45 &  46 &  68  \\
HD~128369, HD~128185 (C1,~C3) & 164 &  58 &  57 &  62 &  85 \\
HD~129430, HD~128185 (C2,~C3) & 141 &  67 &  59 &  66 &  81 \\
HW~CMa \& SW~CMa         &     &     &     &     &     \\
HD~56341, HD~53123 (C1,~C2)   & 536 &  54 &  45 &  48 &  54  \\ 
V636~Cen                  &     &     &     &     &      \\
HD~124829, HD~125444 (C1,~C2) & 388 &  51 &  52 &  54 &  65 \\ 
VZ~Hya                    &     &     &     &     &     \\
HD~72528,  HD~71615  (C1,~C2) & 328 &  37 &  35 &  37 &  59 \\
HD~72528,  HD~72782  (C1,~C3) & 333 &  43 &  36 &  41 &  61 \\
HD~71615,  HD~72782  (C2,~C3) & 335 &  43 &  33 &  36 &  57 \\ 
WZ~Oph                    &     &     &     &     &     \\
HD~155193, HD~154931 (C1,~C2) & 288 &  40 &  38 &  39 &  61 \\
\hline
\end{tabular}
\end{table}