%%
%% The LaTeX Companion, 3ed
%%
%% Example 6-7-17 on page I-486 in "siunitx --- Scientific numbers in tables".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{123.0pt}
\setlength\parindent{0pt}
%StartShownPreambleCommands
\usepackage{siunitx}
%StopShownPreambleCommands

\begin{document}
\begin{tabular}{|S[table-format=2.2e1]|
    S[exponent-mode=fixed,drop-exponent,fixed-exponent=3,
      table-format=2.4]|}
 {Data} & {Data (\num[drop-exponent=false,
                      print-unity-mantissa=false]{e3})} \\
 1.2e3 & 1.2e3 \\ 17.5 & 17.5 \\ 3e2 & 3e2 \\ 1.03e4 & 1.03e4
\end{tabular}
\end{document}