# siunitx removes a decimal zero

I am trying to typeset the value 2.4 +/- 0.009 using the siunitx package and the \num command. However, once I switch siunitx to show the uncertainty with a \pm character, it removes one decimal zero.

MWE:

\documentclass{article}

\usepackage{siunitx}

\begin{document}
\noindent
\num[separate-uncertainty=true]{2.4 \pm 0.009} \\
\num[separate-uncertainty=false]{2.4 \pm 0.009}
\end{document}


Result:

2.40 ± 0.09 (missing one decimal)

2.40(9) (also incorrect, see comment)

Am I making a mistake, or is there something wrong in the siunitx package? Or did I miss a necessary option?

Edit: I apparently misunderstood the meaning of the parenthesis notation, where the number in parenthesis is the ± value for the digit(s) left of it. However, this just means both typesetted values are wrong, and not only the first as I had assumed initially.

Edit 2: I just contacted the package's author. Apparently he is aware of the problem, and as Bernard commented below, consideres the input invalid (since it does not have enough digits for the given uncertainty). However, he will have a look at it.

• Nothing is wrong - you have just misunderstood the notation of uncertainty. en.wikipedia.org/wiki/Uncertainty Apr 17, 2017 at 22:46
• @hpekristiansen: Admittedly, I misunderstood the meaning of the parenthesis notation (will edit this in a second). However, that just means that both results are simply wrong? If I explicitly state to have 2.4 \pm 0.009, I do NOT want anything to change this to 2.4 \pm 0.09, since this isn't a question of notation anymore.
– Timm
Apr 17, 2017 at 22:59
• Ok - I see now. Bernard gives the solution - you need the correct number of digits on the number part of the input. Apr 17, 2017 at 23:03
• There is a bug but the input is defective (there simply are not enough significant digits). Apr 26, 2017 at 21:24

Write \num{2.40\pm 0.009} or \num{2.400 (9)}.