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I would like to use expressions like "< 1 W" in the text to express "less than one Watt". I try to use the siunitx package throughout the whole document to get a consistent look.

There is the option to use \SI{< 1}{\watt} which produces no space between "<" and "1", so I guess this is the recommended typography. However, I would like to do the same for, e.g., "< \lambda/2". When used in math mode this produces a space after "<" and I see no option to use siunitx since I do not want to write "< 1 \lambda/2".

Is there a way to achieve the desired output with siunitx or do I have to remove the space in math mode manually?

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  • @StevenB.Segletes I don't quite understand what connection you suggest to tolerances. Maybe I'll be more specific. I work in physical optics, so here \lambda means "wavelength" which is also used as a unit like "we can measure to one tenth of the wavelength". So at least IMHO it's more natural to write \lambda/2 than 0.5 \lambda. The meaning of "< \lambda/2" should then be clear. From egreg's comments I now think the main question is if there should be a space between a (single) relational symbol such as < and a physical quantity such as \lambda/2 or 1 W. – Cornelius Sicker Feb 22 '17 at 12:43
  • I apologize for misinterpretation. I was thinking you were looking for a shorthand nomenclature for saying "less than [some value]" I will delete my earlier comment, as it misleads the reader. – Steven B. Segletes Feb 22 '17 at 12:47
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You can define a command for that; but I don't think your readers will appreciate.

\documentclass{article}
\usepackage{siunitx}

\newcommand{\lt}{{<}}

\begin{document}

\SI{<1}{\watt}

\SI[parse-numbers=false]{\lt\lambda/2}{\watt}

\end{document}

enter image description here

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  • Maybe my question was ambiguous. I do not want do say "< \lambda/2 W", but "< \lambda/2". So \lambda basically takes the place of the unit, but I find "\lambda/2" better understandable than "0.5 \lambda". Why do you think the readers might not appreciate this? – Cornelius Sicker Feb 22 '17 at 12:12
  • @CorneliusSicker Not sure I understand the connection with siunitx, then. I'd definitely write $<\lambda/2$, with the standard spacing. – egreg Feb 22 '17 at 12:14
  • I want to express a physical quantity, hence I'd like to use siunitx to get consistent output. If you prefer the math mode solution with the space, would you also write $< \SI{1}{\watt}$ (producing a space), rather than \SI{<1}{\watt} (no space)? So maybe it's more a typographical question if the standard way of siunitx to typeset "< some quantity" is correct? – Cornelius Sicker Feb 22 '17 at 12:25
  • @CorneliusSicker If I were to use it, I'd simply type $<\SI{1}{\watt}$, but my mathematician's background might be kicking in. – egreg Feb 22 '17 at 12:27
  • Okay, so it appears to be a matter of taste so far. Thanks nevertheless for providing a way to achieve both versions with siunitx. This question might be related, in spite of having no answer, yet. – Cornelius Sicker Feb 22 '17 at 12:31

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