\begin{table}%t1
\caption {\label{observations}Details of the observations presented in this paper.}
%\centerline
 {\begin{tabular}{cccr}
\hline\hline
Epoch & $\nu$ [GHz] & Array/Survey & Reference \\
\hline
1992.73  &  5.0  & VLBA CJF-Survey  & Britzen et~al. (\cite{Britzen07})  \\
1992.85  & 22.2  & Global array & Bach et~al. (\cite{Bach05}) \\
1993.71  & 22.2  & Global array & Bach et~al. (\cite{Bach05})  \\
1994.21  &  8.4  & VLBA     & Bach et~al. (\cite{Bach05})\\
1994.67  & 15.3  & VLBA MOJAVE/2~cm Survey & Kellermann et~al. (\cite{Kellermann98}); Zensus et~al. (\cite{Zensus02})\\
1994.70  &  5.0  & VLBA CJF-Survey & Britzen et~al. (\cite{Britzen07})  \\
1995.15  &  22.2 & VLBA & Jorstad et~al. (\cite{Jorstad01})   \\
1995.47  &  22.2 & VLBA & Jorstad et~al. (\cite{Jorstad01})    \\
1995.65  &  8.4, 22.2  & VLBA    & Bach et~al. (\cite{Bach05})   \\
1996.34  &  22.2  & VLBA & Jorstad et~al. (\cite{Jorstad01})  \\
1996.53  & 15.3  & VLBA MOJAVE/2~cm Survey & Kellermann et~al. (\cite{Kellermann98}); Zensus et~al. (\cite{Zensus02})\\
1996.63  &  5.0  & VLBA/CJF-Survey & Britzen et~al. (\cite{Britzen07})  \\
1996.82  & 15.3  & VLBA MOJAVE/2~cm Survey & Kellermann et~al. (\cite{Kellermann98}); Zensus et~al. (\cite{Zensus02})\\
1996.90  &  22.2  & VLBA & Jorstad et~al. (\cite{Jorstad01})  \\
1997.03  &  8.4  & VLBA & Fey et~al. (\cite{Fey00}) \\
1997.58  &  22.2  & VLBA & Jorstad et~al. (\cite{Jorstad01})  \\
1997.93  &  8.4  &  VLBA & Ros et~al. (\cite{Ros01}) \\
1999.41  &  8.4  &  VLBA & Ros et~al. (\cite{Ros01}) \\
1999.55  & 15.3  & VLBA MOJAVE/2~cm Survey & Kellermann et~al. (\cite{Kellermann98}); Zensus et~al. (\cite{Zensus02})\\
1999.89  &  5.0  &  VLBA/CJF-Survey  &  Britzen et~al. (\cite{Britzen07}) \\
2000.82  &  5.0  &  VLBA+Effelsberg  & Bach et~al. (\cite{Bach05})\\
2001.17  & 15.3  & VLBA MOJAVE/2~cm Survey & Kellermann  et~al. (\cite{Kellermann98}); Zensus et~al. (\cite{Zensus02})\\
2002.48  &  8.4, 22.2, 43.2 & VLBA$^{*}$  &  Agudo et~al. (\cite{Agudo07}) \\
2003.20  &  8.4, 22.2, 43.2 & VLBA$^{*}$  &  Agudo et~al. (\cite{Agudo07}) \\
2003.49  &  8.4, 22.2, 43.2 & VLBA$^{*}$  &  Agudo et~al. (\cite{Agudo07}) \\
2003.65  & 15.3  & VLBA MOJAVE/2~cm Survey  & Kellermann et~al. (\cite{Kellermann04})\\ 
2003.88  & 22.2, 43.2  &      VLBA  &  Agudo et~al. (A\&A, 2008, in prep.) \\
2004.44  & 15.3  & VLBA MOJAVE/2~cm Survey & Kellermann et~al. (\cite{Kellermann04})\\
2004.60  & 15.3, 22.2, 43.2&  VLBA$^{*}$  & Agudo et~al. (\cite{Agudo07})  \\
2004.79  & 15.3  & VLBA MOJAVE/2~cm Survey  & Kellermann et~al. (\cite{Kellermann04})\\
2004.97  & 15.3, 22.2, 43.2&  VLBA$^{*}$  & Agudo et~al. (\cite{Agudo07})  \\
2005.01  & 15.3  & VLBA MOJAVE/2~cm Survey  & Kellermann et~al. (\cite{Kellermann04}) \\
2005.09  & 15.3, 22.2, 43.2 & VLBA$^{*}$  & Agudo et~al. (\cite{Agudo07})  \\
2005.70  & 15.3  & VLBA MOJAVE/2~cm Survey  & Kellermann et~al. (\cite{Kellermann04})\\
2005.72  & 15.3  & VLBA MOJAVE/2~cm Survey  & Kellermann et~al. (\cite{Kellermann04}) \\
2006.32  & 15.3  & VLBA MOJAVE/2~cm Survey  & Kellermann et~al. (\cite{Kellermann04})\\
\hline
\end{tabular}}
\par
\smallskip
In epochs marked by a star, S5 0716+714 served as calibrator for observations targeted on NRAO~150.  
\end{table}