\begin{table}%t3
   %\centering
\par
   \caption{The results of running 20~sets of simulated data through the parameter fitting program. With the exception of~$f$ all parameters
have units of milliarcseconds per year.\label{parerr}}
\begin{tabular}{cccc}
   \hline\hline
Parameter&Input Value&\multicolumn{2}{c}{Fitted Value}\\
&&Mean&Error\\
\hline
$f$&0.5&0.508&0.025\\
$\sigma$&3.5&3.42&0.10\\
$\mu_{xc}$&0.00&--0.01&0.208\\
$\mu_{yc}$&32.0&32.1&0.2\\
$\tau$&25.0&26.5&5.3\\
$\Sigma_{x}$&10.0&10.0&0.4\\
$\mu_{xf}$&0.0&--0.05&0.475\\
\hline
\end{tabular}
\end{table}