Automatic per-mode switch from symbol to reciprocal

Question

Is there a way to make the siunitx package output a unit with a single slash using per-mode=symbol and fallback to per-mode=reciprocal when there is more than one slash?

\documentclass{article}
\usepackage{siunitx}

\begin{document}
\SI{1}{\metre\per\second}            % would output 1 m/s
\SI{1}{\ampere\per\metre\per\second} % would output 1 A m-1 s-1
\end{document}

Answer 1

Not very automatic, but helpful if you have to write it many times. You can define a new unit like

\DeclareSIUnit\Ms{m/s}

and use it like

\SI{1}{\Ms}

whenever you need.

\documentclass{article}
\usepackage{siunitx}
\DeclareSIUnit\Ms{m/s}
%\sisetup{per-mode=symbol}

\begin{document}
\SI{1}{\metre\per\second}            

\SI{1}{\Ms}            % would output 1 m/s

\SI{1}{\ampere\per\metre\per\second} % would output 1 A m-1 s-1
\end{document}

But if you have other instances of such cases, you have to define one for each of them.