\documentclass[final,letterpaper,twoside,12pt]{article}
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Table~{\ref{tab:ngdata}} shows how to have headings
that don't span all of the columns.
\begin{table}[ht!]
\begin{center}
\begin{tabular}{|c|p{1cm}|p{1cm}|p{1cm}|p{1cm}|p{1.5cm}|} \hline
&\multicolumn{5}{|c|}{Times (seconds)} \\ \cline{2-6}
&\multicolumn{4}{|c|}{Ball one}& Ball two \\ \cline{2-5}
&\multicolumn{4}{|c|}{Technique} &\\ \cline{2-5}
$i$ & $g_A$  & $g_B$ & $d_A$ & $d_B$ & \\ \hline \hline
1 & & & & &   \\
2 & & & & &   \\
3 & & & & &   \\
4 & & & & &   \\
5 & & & & &   \\
\hline \hline
%$\bar{t}$ & & & & &  \\
average& & & & &  \\
\hline
$g$ & & & & &  \\
\hline
\end{tabular}
\end{center}
\caption {Timing data}
\label{tab:ngdata}
\end{table}


\end{document}

