\begin{table}%t1
%\centering
\par
\caption{Normalization constants.}\label{tab1}
\begin{tabular}{@{} c c c l @{}}
\hline\hline
Symbol & Quantity & Constant & Value \\
\hline
$t$      & Time & $\tau_0$  & $=$1~s   \\
$n$      & Number density  & $n_0$  & $=5\times10^{16}$~m$^{-3}$  \\
$T$ & Temperature     & $T_0$  & $=$8400~K  \\
$\rho$   & Density & $\rho_0 = n_0 m_{\rm p}$  & $\approx$$ 8.4\times10^{-11}$~kg~m$^{-3}$ \\
$P$      & Pressure        & $P_0 = n_0 k_{\rm B} T_0$ & $\approx$$ 5.8\times10^{-3}$~Pa \\
$V$      & Velocity        & $c_{0} = (P_0/\rho_0)^{1/2}$   & $\approx$$ 8.3$~km~s$^{-1}$ \\
$x,y,z$  & Length & $\Delta = c_{0} \tau_0$ & $\approx$$ 8.3$~km \\
$B$      & Magnetic field  & $B_0 = (2 \mu_0 P_0)^{1/2}$    & $\approx 1.2\times10^{-4}$~T \\
\hline
\end{tabular}
\end{table}