\begin{table}%t1
%%\centering
\par
\caption{511 $\rm{keV}$ line fit parameters for VDMs before and
after final setting.}  \label{table:fitpars}
\begin{tabular}{|l|c|c|c|c|c|c|} \hline\hline
    & \multicolumn{3}{c|}{Initial settings} & \multicolumn{3}{c|}{After tuning} \\ \cline{2-7}
VDM & Peak   & $\sigma$ &  {\it FWHM} & Peak   & $\sigma$ &  {\it FWHM} \\
    & (chan) & (chan)   & (\%) & (chan) & (chan)   & (\%) \\ \hline
1   & 50.7 & 4.66 & 21.7 & 25.8 & 2.9 & 26.6 \\
2   & 50.3 & 6.7  & 31.3 & 26.6 & 3.3 & 29.4 \\
3   & 53.5 & 5.3  & 23.4 & 27.7 & 4.0 & 34.4 \\
4   & 50.8 & 5.2  & 24.2 & 26.7 & 3.2 & 28.5 \\
5   & 50.7 & 6.3  & 29.2 & 25.6 & 3.2 & 30.2 \\
6   & 46.3 & 6.1  & 31.3 & 25.2 & 3.5 & 32.9 \\
7   & 47.5 & 7.1  & 35.0 & 26.4 & 4.9 & 43.4 \\
8   & 51.7 & 6.5  & 29.8 & 26.7 & 3.3 & 28.6 \\
9   & 51.7 & 4.4  & 20.1 & 26.5 & 2.7 & 24.8 \\
10  & 49.0 & 4.7  & 22.6 & 26.0 & 2.9 & 26.6 \\
11  & --   & --   & --    & 27.4 & 4.0 & 35.0 \\
12  & 55.9 & 5.5  & 23.2 & 25.8 & 3.4 & 31.0 \\
13  & 49.9 & 4.5  & 21.1 & 26.4 & 2.8 & 25.2 \\
14  & 53.6 & 5.9  & 25.9 & 24.4 & 2.7 & 22.8 \\
15  & 50.6 & 5.5  & 25.4 & 25.0 & 3.4 & 31.7 \\
16  & 50.5 & 4.9  & 23.1 & 26.6 & 2.9 & 25.4 \\
Total & 50.9 & 5.8 & 26.5 & 26.3 & 2.9 & 25.9 \\ \hline
\end{tabular}
\end{table}