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I am writing a document that contains formulas like this:

25 Va + 100 Vc = -3000

My colleague tells me that I should write it with a space on the 3000, or with a comma, like this

25 Va + 100 Vc = -3 000

or

25 Va + 100 Vc = -3,000

I never saw formulas written like this. What is the best practice?

BTW, how do I insert equations here? \$ or $$ not working for me...

Duck
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    It mainly depends on the guidelines of the publisher/university you are writing to. If there aren't any, then it comes down to personal preference. I like the siunitx package with group-separator=\, (a small space). (This site doesn't have MathJaX enabled, so $$...$$ wont render the formula.) – Phelype Oleinik May 10 '19 at 19:50
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    mathjax is not enabled on this site, if you want to show output add a screenshot image – David Carlisle May 10 '19 at 19:50
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    Reiterating @PhelypeOleinik suggestionL I would say you should definetly include \usepackage{siunitx} and then say \num{-3000}. Then it will be easy to later change the style to -3,000, or -3 000 with a global switch. I use this for any numbers that are 4 or more digits (including decimal digits). – Peter Grill May 10 '19 at 20:16
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    According to the General Conference on Weights and Measures, a comma or a point should indicate a decimal marker. "Numbers may be divided in groups of three in order to facilitate reading; neither dots nor commas are ever inserted in the spaces between groups". If a publisher declares otherwise, then there is no discussion. As others have mentioned this is easily changed using the siunitx package. – erik May 10 '19 at 20:19
  • NOTE both the NIST guidance and CGPM resolution are trying to encourage ONE universal behaviour for the future In any number there shall be only one decimal marker (Therefore only one comma permitted to show the decimal) but since most users are used to seeing the fullstop it is also acceptable in summary 3,000 = 3.000 three with 3 trailing zeros hence the confusion since many would consider that is 3 000 (3 thousand ) –  May 10 '19 at 23:52

1 Answers1

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Whether you write 3000, 3 000, 3,000, or 3'000 -- or yet something else... -- should probably be determined mostly by any typographic standards in force in the country or area you find doing your work.

The \num macro of the siunitx package is very handy in this regard because it lets you separate content from an particular typographic convention.

enter image description here

\documentclass{article}
\usepackage[group-digits=true,group-minimum-digits=4]{siunitx}
\begin{document}

\num{3000} % default group separator symbol: "thinspace" (\,)

\num[group-separator={,}]{3000} % comma

\num[group-separator={\mbox{'}}]{3000} % apostrophe

\sisetup{group-digits=false} % turn off grouping entirely

\num{3000} 
\end{document}
Mico
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  • very good answer, thanks! – Duck May 10 '19 at 20:49
  • Does that answer also apply to numbers in math mode, as this is what the OP specifically asked for? That is, would you use \num the same way in math mode as you would do in plain text? The linked duplicate also isn't clear about that – siracusa May 10 '19 at 21:35
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    @siracusa - Indeed, \num works in both text and math mode. – Mico May 10 '19 at 21:41