# Siunitx and cancel package

I want to symbolically cancel out units using the siunitx package. To do so I tried the cancel package as in the following minimal example:

\documentclass{article}

\usepackage{amsmath}
\usepackage[per=frac]{siunitx}
\usepackage{cancel}

\begin{document}
\begin{align*}
\frac{\SI{7}{\m}}{\SI{3}{\m}} =  \frac{\SI{7}{\cancel \m}}{\SI{3}{\cancel \m}}
\end{align*}
\end{document}


But this gives me the following output, i.e. when using \cancel the font of the unit changes which is not desired. Any idea how to fix this?

Edit: I tried @percusse's solution which works very well. But if I also add the option expproduct=cdot to the package options, the problem reappears.

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On your edit, you are using v1 option names which forces compatibility mode. Version 1 did not 'know' \cancel, so unsurprisingly it treats things a bit oddly. –  Joseph Wright Oct 21 '12 at 8:28
Ok, thanks. Switching to exponent-product=\cdot worked. –  student Oct 21 '12 at 8:41
Finally the problem was that the documentation of siunitx on my box was not up to date. So I didn't find the option exponent-product as well as per-mode... –  student Oct 21 '12 at 8:42

You are using an old type of option to siunitx. If I fix the option everything is shown as expected. It also warns you to use the version 2 type inputs.

\documentclass{article}

\usepackage{amsmath}
\usepackage[per-mode=fraction]{siunitx}
\usepackage{cancel}

\begin{document}
\begin{align*}
\frac{\SI{7}{\m}}{\SI{3}{\m}} =  \frac{\SI{7}{\cancel\m}}{\SI{3}{\cancel\m}}
\end{align*}
\end{document}


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If I add the option: expproduct=cdot to the package option list, the problem reappears. Any idea? –  student Oct 21 '12 at 8:25
@student Have a look at the list on page 75, you'll see the newer version for that option. (I have the version released on 2012/7/22) –  percusse Oct 21 '12 at 9:51