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What is considered proper typography regarding which set of numerals to use with units of measurement?

A real-life example:

In the experiment, shown schematically in figure 2.2, we illuminate an array of 10 slits, each 50 nm wide, with a laser beam at λ = 830 nm.

Which numerals in the above sentence should be set as oldstyle (text) numerals and which should be lining numerals? As far as I know,

  • "figure 2.2" should be oldstyle in any case.
  • "10 slits" should also be oldstyle.
  • for "50 nm wide", a case could be made for either one. Personally I think oldstyle looks better here.
  • for "λ = 830 nm", the answer should be the same as "50 nm wide". But this is even more of a grey area, since strictly speaking the "830 nm" is part of an equation. If it were "f/2 = 50 Hz" then I would definitely want the "2" to be a lining numeral.

Also, is using the siunitx package macros for every instance of a number followed by a unit of measurement the best way to achieve this?

ADDENDUM

Unfortunately using siunitx gives me the dreaded Too many math alphabets error and I'm not wasting any more precious hours of my life fixing that one. Here are the macros that have always worked well enough for me:

\newcommand{\unit}[1]{\mbox{$\;\mathrm{#1}$}}
\newcommand{\micron}{\mbox{$\;\text{\textmu m}$}} % special case of \unit
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4  
Be consistent. If you use lining numerals before one unit of measure, then all should be lining. And I'd prefer "an array of ten slits". –  egreg Oct 24 '12 at 13:16
1  
As I came across Don't ask us about best practices, glom of nit, or Mrs Cake quite parallel to reading your question, I had to smile. –  Benedikt Bauer Oct 24 '12 at 13:17
    
    
@BenediktBauer I looked at that post to try to determine whether this question was appropriate. But it's one of the most confusing meta questions I've ever seen. For one thing, I'm not a Discworld buff so I had to google "glom of nit" and "Mrs Cake", and even now I have no idea why we can't ask about them. The only thing I got out of it was to solicit advice rather than ask about best practices, which I tried to do in the above question. –  ptomato Oct 25 '12 at 13:14
    
@ptomato To me it still looked like a best practices question. While I was thinking about this comment here, there came a simple and interesting trick into my mind, which should very easily allow to check if the question comes close to a best practices question: If can sum up your question as "I want to achieve x by means of y (maybe additional "because of z"), how do I get this?" then it is quite surely not a best practices question. –  Benedikt Bauer Oct 25 '12 at 13:41

2 Answers 2

up vote 12 down vote accepted

Personally, I prefer to set any numbers with units as maths, leading to something like:

In the experiment, shown schematically in figure 2.2, we illuminate an array of 10 slits,
each $50~\mathrm{nm}$ wide, with a laser beam at $\lambda = 830~\mathrm{nm}$.

math

It makes things consistent: you shouldn't use old style numerals in maths and you should include units as much as possible. Something like this looks a bit confusing to me:

weird

The siunitx package just makes it easier to be consistent:

In the experiment, shown schematically in figure 2.2, we illuminate an array of 10 slits,
each \SI{50}{nm} wide, with a laser beam at $\lambda = \SI{830}{nm}$.

siunitx

Now, this might also look inconsistent - first there is an old style 10, and then there is a lining 50. In these situations I prefer to just write 'ten' or not to use old style numerals at all.

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Best answer so far, and most consistent. –  ptomato Nov 6 '12 at 10:13
    
This is exactly what I had decided to do, I'm glad someone else thinks the same way. –  Mk12 May 19 '13 at 20:11

I don't think using mathmode to write lining numbers in the text is the right approach. It only works properly if your math- and text font are identical.

If we follow Bringhurst's Elements of Typographical Style (and we should): "Use titling [lining] figures with full caps, and text [oldstyle] figures in all other circumstances" (p. 321).

So the recommendation is always to use oldstyle figures in text. I personally use:

  • Proportional OSF in text
  • Proportional Lining for math
  • Proportional Lining fur full caps
  • Monospaced OSF in tables

In order to achieve this you need a full font, e.g. Minion Pro, using the MinionPropackage, or the now obsolete libertine-legacy package. It is also easy to set up with fontspec using XeLaTeX/LuaLaTeX and an appropriate font.

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