\begin{table}%t1
%\centering
\par
\caption{RMS after each step in the scanner-distortion
correction.
\label{table:1}}
\begin{tabular}{l c c}
\hline\hline
Step & rms $x$ ($\mu\rm  m$)& rms $y$ ($\mu \rm m$) \\
\hline
 Initial (uncorrected) & 31.2 & 32.9 \\
 1-d function corrected  & 18.2 & 23.0 \\
 Correction cubic pattern & 4.61 & 4.42 \\
 2nd iteration cubic pattern & 4.52 & 4.31 \\
\hline
\end{tabular}
\end{table}