\begin{table}%t6
%\centering
\par
\caption {\label{tab_vr_millenium}Number counts for $m_{\rm AB}\le25.5$ and field to field uncertainties
  ($v_r$) calculated from the Millenium simulation in a $6\arcmin \times 6\arcmin$ blank
  field, for different source redshifts.} 
\begin{tabular}{cc c c} 
\hline\hline
\noalign{\smallskip}
      & $z_{\rm s}=6$ & $z_{\rm s}=7$ & $z_{\rm s}=8$ \\
\hline
$\langle N \rangle$ & 2.74 & 1.10 & 0.39 \\
$v_{r}$ & 68\% & 100\% & 168\% \\
\hline
\end{tabular}
\end{table}