\begin{table}%t6
%\centering
\par
   \caption{Grism parameters, their default values, and required
     units.}
   \label{ta:griparms}
   \begin{tabular}{lcc}
      \hline\hline
      Keyword & Default & Units \\
      \hline
      \PVk{0} = $G$         & 0 & m$^{-1}$ \\
      \PVk{1} = $m$         & 0 &          \\
      \PVk{2} = $\alpha$    & 0 & deg  \\
      \PVk{3} = $n\sub{r}$  & 1 &          \\
      \PVk{4} = $n'\sub{r}$ & 0 & m$^{-1}$ \\
      \PVk{5} = $\epsilon$  & 0 & deg  \\
      \PVk{6} = $\theta$    & 0 & deg  \\
      \hline
   \end{tabular}
\end{table}