[Tex/LaTex] Why do the standard siunitx settings not detect font weight

siunitx

Using KOMA-script I got a bold font for chapter/section titles. I had a unit, \SI{1}{\something}, in one of them which was not set in bold font. Giving siunitx the following options

detect-weight=true, detect-family=true

helped. Probably there are good reasons not to enable this by default. Which are they?

Best Answer

The aim of siunitx is to be a flexible and comprehensive units package which follows the 'standards' as far as possible when loaded. If you read up on the use of units, you'll find that quantities (the combination of a number and a unit) is a mathematical entity. As with other mathematics, things like font shape and weight are therefore important. With the default settings, the package uses the current upright roman font for everything: that's the same as any other mathematics:

\textbf{Bold text but $y = mx + c$}

However, some people prefer to follow some or all of the surrounding style, particularly in section headings. That's where the 'flexible' part comes in: you can do that using a package option without otherwise changing the input.

Related Solutions

[Tex/LaTex] siunitx does not detect typeface and size

The class doesn't use nfss to define fonts and so siunitx has absolutly no chance to detect the font (and as a side-warning: be careful with non-ascii chars. In the combination with xelatex/lualatex they can come out wrong or be missing all together). You can get around the problem by redefining the font commands:

\documentclass{pnastwo}

\usepackage{graphicx}
\usepackage{amssymb,amsfonts,amsmath}
\usepackage{gensymb,fixltx2e}
\usepackage{fontspec}
\renewcommand\materialfont{\sffamily\fontsize{7pt}{\baselineskip}\selectfont}
\usepackage{siunitx}
\sisetup{detect-weight=true, detect-family=true}

\begin{document}
\begin{article}
\begin{materials}
This is a minimal example. The following units \SI{15}{\mL} do not render with the same typeface and size as the surrounding text.
\end{materials}
\end{article}
\end{document}

[Tex/LaTex] Font settings in siunitx package

The \SI macro in siunitx has optional parameters (list of key-value pairs). One of the keywords is 'mode', with possible values 'text', 'math'. You may have to set 'detect-mode' to false in \sisetup.
If you want to always use the math fonts for your measures/units, then you can use

\sisetup{mode=math}

This is explained in the documentation of the siunitx package. You can also select the math fonts with other package macros. Full exemple (note that I use LuaLatex):

\documentclass[a4paper,article,openany,12pt]{memoir}
\usepackage{lipsum}
\usepackage{mathpazo} %shows the differences between math and text mode better
\usepackage{fontspec}
\usepackage{siunitx}


\begin{document}
\sisetup{mode=math}    

\SI[mode=text]{9.8}{\kilogram\metre\per\second\squared}\\
\SI{9.8}{\kilogram\metre\per\second\squared}\\
$\SI{9.8}{\kilogram\metre\per\second\squared}$

\end{document}

Best Answer

Related Solutions

[Tex/LaTex] siunitx does not detect typeface and size

[Tex/LaTex] Font settings in siunitx package

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