\documentclass{article}

\usepackage{booktabs}
\usepackage{siunitx}

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\begin{document}

\begin{tabular}
  {
    @{}
    >{$}l<{$}
    S[table-format=-2.3(1)]
    S[table-format=3.3(1)]
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  \toprule
  {\text{Parameter}} & {First} & {Second} \\
  \midrule
  a / \si{\angstrom} & 1.234(2) & 5.678(4) \\
  \theta / \si{\degree} & -90.34(4) & 104.45(7) \\
  q / \si{\micro\meter} & 0.532 & 0.894 \\
  \gamma / \si{\per\kilo\gram} & 2.734 & 1.485 \\
  \bottomrule
\end{tabular}

\end{document}
