# Using siunitx, \ohm results in an italic Omega

The title basically says it all.

I use siunitx with

\usepackage[binary-units=true]{siunitx}
\sisetup{locale = DE}


For \SI{...}{\micro\ohm}, the \micro is output correctly (non-italic), and \ohm is output in italic. This happens both in text and in math mode.

My MWE is

\documentclass{publisher-custom}
\usepackage[binary-units=true]{siunitx}
\sisetup{locale = DE}

\begin{document}
\SI{1,09715247}{\micro\ohm}
\end{document}


How can I fix this as I'm unable to change (or post here) what's in the publisher's custom document class code?

Update:

I found these lines in the publisher's cls file grep'ing for [Oo]mega:

...
\DeclareMathSymbol{\Omega}{\mathalpha}{letters}{"0A}
...
\DeclareMathSymbol{\varOmega}{\mathalpha}{operators}{"0A}
...


Does that help?

• You really should post a MWE here: I can't reproduce your output. Plus, the macro you should use is \micro, not plain \mu. – campa Aug 20 '15 at 13:22
• Without the class publisher-custom the MWE will already on the first line. If you cannot make the class available, then use a standard class and add the stuff of the class, which is needed to reproduce the problem. My first guess would be font related stuff. – Heiko Oberdiek Aug 20 '15 at 13:52
• Try if you can do %\DeclareMathSymbol{\Omega}{\mathalpha}{letters}{"0A} (comment out that line)! If you can still compile, you are good to go. – LaRiFaRi Aug 20 '15 at 13:56
• LaRiFaRi: That works, but I need a solution that does not tinker with the cls file. – apriori Aug 20 '15 at 14:02
• What about \DeclareMathSymbol{\Omega}{\mathalpha}{operators}{"0A} then? Seems to be a duplicate of Force upright Greek letters with isomath – moewe Aug 20 '15 at 14:09

## Answer to the updated question

The special class file uses:

\DeclareMathSymbol{\Omega}{\mathalpha}{letters}{"0A}
\DeclareMathSymbol{\varOmega}{\mathalpha}{operators}{"0A}


Then \Omega is italics by default and \varOmega upright. Package siunitx uses \upOmega, if it is available to initialize the symbol for math-ohm, otherwise \Omega is used as \text{$\Omega$}, which results in an italics Ω. Whereas \mathrm{\Omega} would have given an upright Ω.

Since the upright ohm symbol is available as \varOmega, the macro \upOmega can be provided easily for package siunitx:

\documentclass{article}
\DeclareMathSymbol{\Omega}{\mathalpha}{letters}{"0A}% italics
\DeclareMathSymbol{\varOmega}{\mathalpha}{operators}{"0A}% upright
\providecommand*{\upOmega}{\varOmega}% for siunitx
\usepackage[binary-units=true]{siunitx}
\sisetup{locale = DE}

\begin{document}
\SI{1,09715247}{\micro\ohm}
\end{document}


## Answer to the first version of the question

I get an italic \mu. Probably you want to have \micro instead. The \ohm is upright:

\documentclass{article}
\usepackage[binary-units=true]{siunitx}
\sisetup{locale = DE}
\begin{document}
\si{\mu\ohm} vs.\@ \si{\micro\ohm}
\end{document}


• \usepackage{lmodern} would be nice here. – LaRiFaRi Aug 20 '15 at 13:29
• @LaRiFaRi Why? Basically I get the same result. Also I did not want to add additional font packages to keep the example minimal. I suspect some problem with the fonts, which are used by the OP. – Heiko Oberdiek Aug 20 '15 at 13:43
• Just zoom in and take a look on the \micro. But, never mind. You got my vote. Let's wait for the OP's update. – LaRiFaRi Aug 20 '15 at 13:54
• @LaRiFaRi If I compare the result of \showlists, then there are tiny changes in the bounding box of \micro, but the shape looks pretty much the same with the ugly serifs, especially at the bottom. – Heiko Oberdiek Aug 20 '15 at 14:01
• @LaRiFaRi I see, siunitx already uses T1 encoding, thus you need to install cm-super. – Heiko Oberdiek Aug 20 '15 at 14:41

The designer of your document-class wants you to have italic upper-case Greeks which in my eyes is desirable according to ISO (but of course a matter of taste).

As your template is written as it is, I would not change this behaviour as I have suggested in comment. Just redefine the math-ohm from siunitx like so:

% arara: pdflatex

%\documentclass{publisher-custom}
\documentclass{article}
\usepackage{siunitx}
\sisetup{%
,binary-units=true
,locale = DE
,math-ohm  =\Omega
}
\usepackage{lmodern}
\si{\micro\ohm} and $\si{\micro\ohm}$ but $\mu\times\Omega$

• That works! But I fail to comprehend why it does. According to the siunitx documentation, math-ohm is by default defined to \Omega. – apriori Aug 20 '15 at 15:24