\begin{table}%t1
\caption{\label{tab:dphicompa}Mean errors in the gravitational acceleration.}
\small%\centering
\par
\begin{tabular}{ccccc}
\hline\hline\noalign{\smallskip}
  \multirow{2}{*}{Component} 
& \multicolumn{2}{c}{Prolate spheroid} 
& \multicolumn{2}{c}{Sphere} 
\\  
 & Poisson solver & extended Poisson solver & 
   Poisson solver & extended Poisson solver \\
\hline \noalign{\smallskip}
 ${\bf \hat{r}}$ & $4.821\times 10^{-4}$ 
                        & $4.698\times 10^{-4}$ 
                        & $1.598\times 10^{-2}$
                        & $1.557\times 10^{-2}$ \\
 ${\bf \hat{\theta}}$ & $6.134\times 10^{-2}$ 
                             & $2.592\times 10^{-2}$ 
                             & $1.67 \times 10^{-2}$
                             & $1.67 \times 10^{-2}$ \\   
 ${\bf \hat{\phi}}$ & $1.245\times 10^{-2}$ 
                           & $2.435\times 10^{-3}$ 
                           & $1.655\times 10^{-2}$ 
                           & $1.655\times 10^{-2}$ \\                 
\hline 
\end{tabular}
\end{table}