\documentclass[a4paper,10pt]{letter}
\usepackage[utf8]{inputenc}
\usepackage{siunitx}
%opening
\title{latexdiff test of siunitx}

\begin{document}
\num{1}

\numlist{1;12;14}

\numproduct{10x1}

\numrange{5}{1}

\ang{23}

\unit{\um}

\qty{20}{\um}

\qtylist{10;20;35}{\cm}

\qtyproduct{10x12}{\square\second}

\qtyrange{12}{15}{\cm}

\complexnum{15+3i}

\complexqty{10+i2}{\cm}


\end{document}