# Chemical purity and siunitx clash when putting a “+” after percentage

I'm using siunitx to describe some chemical purities. The purity I would like to describe is sold by the chemical company as 99.9+ % (not the best way of describing it I'm sure). When I try to describe this using siunitx it halts pdflatex.

\SI{99.9+}{\percent}


Is there a way around this problem with siunitx?

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I don't get errors with \SI[parse-numbers=false]{99.9+}{\percent}, but it doesn't seem a mathematically correct way of writing this: why not at least \SI{99.9}{\percent}? –  egreg Jan 18 '12 at 23:51
@egreg: That may be delving into political chemistry... of course, something we're removed from. –  Werner Jan 19 '12 at 0:08
Instead of the unusual 99.9+ % notation, you could say \SI{>=99.9}{\percent}, which will give you the properly formatted and more mathematically correct output ≥99.9 %. But if you need to reproduce exactly what the manufacturer told you, egreg's suggestion of switching off the number parser is probably the way to go. –  Jake Jan 19 '12 at 2:05
I (used to) work with noble gases. Some of these have a purity of 99.998% or 99.999%. This is a bit messy so a gas purity shorthand developed: 5.0 =99.999% and 4.8=99.998% ie 5 nines and and 4 nines and an eight. I have only seen it used with gases...Is there a 4.9? Does this equal 5.0???!!! –  Leeser Jan 19 '12 at 14:15
Thanks for the help guys. Unfortunately the people at the chemical company state the purity as 99.9+%. As much as it hurts my eyes I need to state it as it is on the bottle. @egreg If you make that into an answer I'll accept it. Thanks. –  Darling Jan 20 '12 at 0:20

The option to use is parse-numbers=false. However there are perhaps slightly better ways to render the symbol (or less bad):

\documentclass[convert,varwidth,border=2]{standalone}
\usepackage{siunitx}
\newcommand{\smallplus}{\raisebox{.3ex}{$\mkern1mu\scriptstyle+$}}
\newcommand{\smallerplus}{\raisebox{.45ex}{$\mkern1mu\scriptscriptstyle+$}}
\begin{document}
\SI[parse-numbers=false]{99.9+}{\percent}

\SI[parse-numbers=false]{99.9\smallplus}{\percent}

\SI[parse-numbers=false]{99.9\smallerplus}{\percent}
\end{document}


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Another possibility would be to add the sign to the list of allowed symbols:

\documentclass{article}
\usepackage{siunitx}
\newcommand\plus{+}
% egreg's nicer versions:
\newcommand\smallplus{\raisebox{.3ex}{$\mkern1mu\scriptstyle+$}}
\newcommand\smallerplus{\raisebox{.45ex}{$\mkern1mu\scriptscriptstyle+$}}

\sisetup{
input-protect-tokens=\plus\smallplus\smallerplus,
input-symbols=\plus\smallplus\smallerplus
}

\begin{document}

\SI{99.9\plus}{\percent}

\SI{99.9\smallplus}{\percent}

\SI{99.9\smallerplus}{\percent}

\end{document}

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