# Best practice for typesetting physical quantities using siunitx [closed]

Consider the following example.

Code

\documentclass{article}

\usepackage{amsmath}
\usepackage[
locale=DE,
output-product=\cdot,
product-units=single % I use this option a lot in the document, so I've defined it globally.
]{siunitx}

\begin{document}

\begin{align*}
A_a
&= A_b - 4 \cdot A_c\\
&= \SI[product-units=repeat]{1900 x 1500}{\mm} - 4 \cdot \frac{1}{2} \cdot \SI[product-units=repeat]{250 x 250}{\mm}\\
&= \SI[product-units=repeat]{1.9 x 1.5}{\m} - 2 \cdot (\SI{0.25}{\m})^{2}\\
&= \num{1.9} \cdot \SI{1.5}{\square\m} - \SI[parse-numbers=false]{2 \cdot 0{,}25^{2}}{\square\m}\\
&= \SI[parse-numbers=false]{(2{,}85 - 0{,}125)}{\square\m}\\
&= \SI{2.725}{\square\m}.
\end{align*}

\end{document}


Output

Question

What is the 'best' way to typeset this using the siunitx package?

Update

Taking Jake's comments into consideration, I write

\num{1.9} \cdot \SI{1.5}{\square\m}


but isn't

\SI[product-units=single]{1.9 x 1.5}{\square\m}


better in this case, since the 1.9 comes from the quantity 1.9 m where there is a unit involved?

## closed as too broad by Adam Liter, ChrisS, Peter Jansson, moewe, GuidoMar 30 '14 at 11:13

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• The way you type it now already seems pretty good to me (except maybe the product-units=single in your preamble). Do you have something particular in mind that you're unhappy with? – Jake Apr 28 '13 at 19:18
• @Jake Not really. I would just like to get different views on the subject. P.S. The product-units=single option is used because I use it often in the 'real' document. – Svend Tveskæg Apr 28 '13 at 19:22
• Sorry, I should have been clearer about the product-units=single thing: You did mention that you use it ofen in the real document, but I think that that's actually bad practice (I believe Joseph Wright would agree), because it's typically incorrect to not repeat the unit (and in the cases where it's not, the product shouldn't be part of the \SI command, because it doesn't syntactically belong with the unit). – Jake Apr 28 '13 at 19:29
• Regarding your last point: I believe the "proper" way to use siunitx here would be to say \SI[product-units=power]{1.9 x 1.5}{\m}, which yields 1.9 x 1.5 m^2 (so the unit in the second argument is applied to both factors of the product, in the same way as it happens with the default setting product-units=repeat) – Jake Apr 29 '13 at 1:44
• Concerning the question whether you should write "1900 mm" or "1.9 m": This depends on how well you know the values. If you are sure, that your measurement has an error smaller than a mm, you can go with the first option. Otherwise go for an option with less significant figures (en.wikipedia.org/wiki/Significant_figures) – user36296 Sep 9 '13 at 17:08