\begin{table}%t5
\caption{\label{tab:syserr}Summary of systematic and statistical uncertainties in the Crab spectrum.}
\small%\centerline
 {
 \begin{tabular}{rc|c|cccc|ccc|cccc|c}
 \hline
 \hline
 $\lambda$ & $E$ &   a   &   b   &   c   &   d   &   e   &   f   &   g   &   h   &   i   &   j   &   k   &   l    &  m \\
 \AA\      & keV &       &       &       &       &       &       &       &       &       &       &       &        &    \\
\hline
 5 & 2.5         & 0.1   & 0.008 & 0.003 & 0.000 & 0.000 & 0.001 & 0.001 & 0.003 & 0.050 & 0.000 & 0.30  & 1.0    & 0.0031 \\
 7 & 1.8         & 0.1   & 0.011 & 0.005 & 0.000 & 0.003 & 0.002 & 0.002 & 0.000 & 0.010 & 0.001 & 0.04  & 0.022  & 0.0025 \\
10 & 1.2         & 0.1   & 0.015 & 0.007 & 0.001 & 0.005 & 0.004 & 0.002 & 0.004 & 0.004 & 0.002 & 0.01  & 0.010  & 0.0025 \\
15 & 0.8         & 0.1   & 0.019 & 0.010 & 0.001 & 0.000 & 0.006 & 0.010 & 0.008 & 0.005 & 0.002 & 0.00  & 0.008  & 0.0026 \\
20 & 0.6         & 0.1   & 0.022 & 0.011 & 0.002 & 0.005 & 0.007 & 0.001 & 0.010 & 0.015 & 0.001 & 0.00  & 0.008  & 0.0045 \\
25 & 0.5         & 0.1   & 0.024 & 0.013 & 0.002 & 0.005 & 0.009 & 0.003 & 0.012 & 0.020 & 0.001 & 0.00  & 0.008  & 0.0048 \\
30 & 0.4         & 0.1   & 0.026 & 0.014 & 0.003 & 0.002 & 0.010 & 0.001 & 0.014 & 0.050 & 0.000 & 0.00  & 0.010  & 0.0090 \\
\hline
\multicolumn{2}{c|}{type}
                 &   c   &   c   &   c   &   c   &   u   &   c   &   c   &   c   &   u   &   c   &   u   &   u    & u \\
\multicolumn{2}{c|}
{$\Delta\alpha$} & 0.016 & 0.010 & 0.006 & 0.002 & 0.001 & 0.005 & 0.001 & 0.010 & 0.010 & 0.000 & 0.027 & 0.006  & -- \\
\multicolumn{2}{c|}
{$\Delta A$}     & 0.100 & 0.019 & 0.010 & 0.001 & 0.001 & 0.004 & 0.005 & 0.004 & 0.003 & 0.002 & 0.005 & 0.002  & -- \\
\hline
\end{tabular}}
\medskip
{\it Main power-law}: $^a$ uncertainty in the K01 continuum model. \\
{\it Curvature corrections}: $^b$~a 50\% change in the lower energy of the 2$-$8~keV range used for the normalisation of the Chandra data; $^c$~break size $\Delta\Gamma=0.006$ at low~$E$ if a break (at 4~keV) is present in the Kuiper et~al. data; $^d$~0.5\% of the absorption with $N_{\rm H}$ 
higher by $7.5$~$\times$ $10^{24}$~m$^{-2}$; $^e$~numerical approximation of $f_{\rm c}(E)$ by~(\ref{eqn:fc}). \\
{\it Interstellar absorption}: $^f$~systematic uncertainty in the dust model; $^g$~neglect of hot gas; $^h$~interstellar carbon abundance. \\
{\it Instrumental corrections}:  $^i$~cross-dispersion correction; $^j$~pile-up correction for 2~CCD mode; adopts 5\% uncertainty in $a$ ($2\sigma$); $^k$~redistribution errors, estimated from difference fit residuals RGS1 and~RGS2; $^l$~errors in the Chebychev polynomials used for the effective area correction; $^m$~typical combined RGS1/RGS2 statistical uncertainty for a full 1~\AA~wide~bin.
\end{table}