# Plus-minus sign messes with mhchem's \pu command

The following bug report has been fixed, here is screenshot of the question in its original state.

Explicit error values are usually given as an interval with $\pm$. When I try to typeset this with mhchem's \pu{...} command, it sneaks some undefined markers in there and raises numbers in a funny fashion:

• $\pu{8.001 \pm 0.005 nm}$
\pu{8.001 \pm 0.005 nm}
• $\pu{8.001 +/- 0.005 nm}$
\pu{8.001 +/- 0.005 nm} (alternative input possibility)
\pu{8.001 +- 0.005 nm} (even easier)
\pu{8.001+-0.005 nm} (thinkable, lesser code readability)

I believe it should rather look like

• $8.001 \pm 0.005~\mathrm{nm}$
8.001 \pm 0.005~\mathrm{nm}

Current workaround would be only typesetting the unit in the command, which kind of defeats the automatic spacing feature:

• $8.001 \pm 0.005~\pu{nm}$
8.001 \pm 0.005~\pu{nm}

Similarly exponents break:

• $\pu{10^-10 m}$ \pu{10^-10 m}
• or worse: $\pu{7.8\times10^-10 m}$ \pu{7.8\times10^-10 m}
• still: $\pu{7.8\times10^{-10} m}$ \pu{7.8\times10^{-10} m}
• Scientific notation works though: $\pu{7.8E-10 m}$ \pu{7.8E-10 m}

I don't know to whether there would be other formats like this, that potentially also break. (Please leave a comment.)

MathJax/mhchem 3.0.6 should fix the issues. It supports all standard uncertaincy notations as listed at https://chemistry.stackexchange.com/a/58667/24052. It will take a week or so to make its way to here.

You can test this not-yet-released version at the bottom of https://mhchem.github.io/MathJax-mhchem/

Thanks! Some of the things are already fixed on my harddrive (the "undefined" error), but not published yet. The others, I take as valid input for my todo list.

For now, 10^-10 can be written as e-10, but I'll support explicit exponents.

What does $8.001 \pm 0.005~\mathrm{nm}$ mean? Shouldn't it rather read $(8.001 \pm 0.005)~\mathrm{nm}$? I am not sure if I should support \pu{7.8\times10^-10 m}. Basically, you are asking for a <any mathematical expression><unit> syntax? Up to now I only had <number><unit> in mind. I am not sure how I could reliably differentiate between mathematical expression and unit ('$5n~\mathrm{g}$' vs. '$5~\mathrm{ng}$').

• Please have a look at Loong's answer. It seems like the \pm variations are not a good choice. However, we'll find them still quite frequently in (especially older) publications, therefore I'd think we might want to support it just for quoting purposes. Anyway, the recommended $\pu{8.001(5) nm}$ \pu{8.001(5) nm} is also broken. Mar 2 '17 at 8:45
• ?? 10^-10 renders as $\ce{10^-10}$ with \ce and $10^-10$ with mathjax
– MaxW
Mar 2 '17 at 17:55