# Round numbers while using plus/minus sign

I'm working currently with the siunitx-package and I would like to use scientific-notation mode, while rounding the numbers. It all works well until I use the \pm command to seperate the uncertainty from the value.

What I mean is using that code:

\documentclass{article}

\usepackage{siunitx}

\sisetup{%
scientific-notation = true,
separate-uncertainty,
}

\newcommand{\roundon[1]}{\sisetup{round-mode = places, round-precision = #1}}
\newcommand{\roundoff}{\sisetup{round-mode = off}}

\begin{document}

\roundon[2]
\SI{1,324 e-5}{\metre}

\end{document}


everything works well. But if I try the following

\SI{1,324 \pm 0,053}{\metre}


it won't work. It's compiling but the numbers aren't rounded anymore.

• I'm not sure rounding makes sense when the uncertainty is given. Jun 21, 2015 at 14:55
• Suppose I have the value and the uncertainty given but in different formats as in 1,23568 and 0,056. Then it is kind of useful Jun 21, 2015 at 15:28
• What should 1,23568 ± 0,056 mean? You can't give a measure with five decimal digits and also that the uncertainty affects the third digit. If the uncertainty affects the third digit, the main measure cannot have more than three. Jun 21, 2015 at 15:31
• That's why I'd like to round it. Given 1,23568 and 0,056 I'd like to have a result like: 1,236 +- 0,056 Jun 21, 2015 at 15:47
• @janfer Still meaningless: you presumably want 1.24(6) = 1.24 \pm 0.06. However, siunitx leaves this well alone: needs a human judgement on the meaning of the numbers. Jun 21, 2015 at 15:50

As Joseph Wright explains in his comment, siunitx does not attempt to handle this, because human judgement is needed in deciding what the numbers mean and how to round them.