# Expressing capital M for molar in siunitx package

The following code isn't valid but conveys my intention:

\SI{}{\micro\molar}

as in micro followed by a big M. I don't want to use the explicit form of micro moles per L raised to the negative one in this case.

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See groups.google.com/group/comp.text.tex/browse_thread/thread/… for a near-identical question posed earlier today on comp.text.tex and an answer by Joseph Wright. –  Mico Sep 6 '11 at 0:10
Which I quoted in my answer. :-) –  Alan Munn Sep 6 '11 at 0:42
The timing is truly a remarkable coincidence! Given this is a relatively obscure question too. –  ptrcao Sep 6 '11 at 3:24

Joseph Wright just answered a similar question on comp.text.tex:

Take a look at the section 'loading additional units' in the manual. In version 1, I did include \molar and \Molar, but tightened up on sticking to SI units (almost) exclusively for version 2. The suggested definitions are

\DeclareSIUnit\molar{\mole\per\cubic\deci\metre}
\DeclareSIUnit\Molar{\textsc{m}}
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So do I have to declare M myself, is that what this means? –  ptrcao Sep 6 '11 at 0:59
Yes. Using the second definition will then provide a \Molar command that can be used like any other regular SI units. So in your example, you would write \SI{}{\micro\Molar} to get the output you asked for. –  Alan Munn Sep 6 '11 at 1:03
Where do I put the custom file siunitx.cfg? –  ptrcao Sep 6 '11 at 1:05
I would put it in <path-to-local-texmf>/tex/latex/siunitx. (i.e. your local texmf directory.) –  Alan Munn Sep 6 '11 at 1:09
@ptrcao Take a look at this question: Where do I place my own .sty files. You need to put them in your local texmf folder, not in C:\texlive... –  Alan Munn Sep 6 '11 at 2:53