\begin{table}%t8
\caption{\label{tab8}Observed polarization angle, in degrees, from a sample of sources measured at 6~cm at Effelsberg during 2007.}
%\centerline
 { \begin{tabular}{llrrrrrrrrrrrrrr}
\hline\hline
& & Feb. & & Apr. & & May & & Jun. & & Aug. & & Nov. & & Dec. & \\
Source & &  PA & $\sigma$ & PA & $\sigma$ & PA & $\sigma$ & PA & $\sigma$ & PA & $\sigma$ & PA & $\sigma$ & PA & $\sigma$ \\
\hline
0743$-$00$^g$ & & 29.5&0.4&31.4 & 0.2 & 32.2 & 0.3 & 28.1&0.4 &30.6& 0.2&31.0 & 1.0 & 26.0 & 0.6 \\
0743$-$00$^h$ & & 28.8 & 1.8 & 30.6 & 2.1 & 31.8 & 1.4 & 29.6 & 1.4 & 29.8 & 1.2 & 34.4 & 2.3 & 24.6 & 7.5 \\
1253$-$05$^g$ & 3C~279  & --28.9 & 0.1 & --28.7 & 0.2 & --36.5 & 0.4 & --17.7 & 0.4 & --1.3 & 0.4 & 12.0 & 0.5 & 9.6 & 0.8 \\
1253$-$05$^h$ & 3C~279  & --29.9 & 0.6 & --28.8 & 1.3 & --31.6 & 1.7 & --17.9 & 0.6 & --1.9 & 1.0 & 13.5 & 0.5 & 8.6 & 0.1 \\
1519$-$27$^g$ & & -- & -- & 3.3 & 0.1 & --34.3 & 0.1 & --36.4 & 0.2 & -- & -- & 130.1 & 0.3 & -- & -- \\
1519$-$27$^h$ & & -- & -- & 2.2 & 0.3 & --28.1 & 6.6 & --36.6 & 0.1 & -- & -- & 129.4 & 1.8 & -- & -- \\
\hline
\end{tabular}}
\medskip
$^g$ Results obtained with the new calibration procedure; $^h$ results obtained with the traditional calibration procedure.
\end{table}