[Tex/LaTex] Siunitx numbers within units preventing cdot use

siunitxunits

I'm using siunitx to handle my units for some notes I'm writing but am having a bit of trouble with defining units for glomerular filtration rate (a measure of kidney function). This is measured in ml/min/1.73m^2 for historical reasons, which I want to render as ml·min·1.73m^-2. I have attempted to define this in the MWE below.

\documentclass[10pt,a4paper]{book}

\usepackage[inter-unit-product=\ensuremath{{}\cdot{}}]{siunitx}

\newcommand{\mlkh}[1]{\SI{#1}{\milli\litre\per\kilo\gram\per\hour}} % for e.g. urine output
\newcommand{\gfr}[1]{\SI{#1}{\milli\litre\per\minute\per\text{1.73}\metre\squared}} % for eGFR

\begin{document}

The patient had a urine output of \mlkh{1.0}.

His GFR was estimated at \gfr{90}.

\end{document}

Output:

Here the first command (\mlkh) works as I expect and gives output with reciprocal units and centre dots but the second command (\gfr) uses slashes to separate the units and is not reciprocal.

Can anyone point out what I'm doing wrong? Is it the presence of the \text{1.73} which is problematic or am I doing something more basic wrong?

Many thanks.

Best Answer

I have no problem if using \sisetup:

\documentclass[10pt,a4paper]{book}

\usepackage{siunitx}
\sisetup{inter-unit-product=\ensuremath{{}\cdot{}}}

\DeclareSIUnit{\strange}{\num{1.73}\,m}

\newcommand{\mlkh}[1]{\SI{#1}{\milli\litre\per\kilo\gram\per\hour}} % for e.g. urine output
\newcommand{\gfr}[1]{\SI{#1}{\milli\litre\per\minute\per\strange\squared}} % for eGFR

\begin{document}

The patient had a urine output of \mlkh{1.0}.

His GFR was estimated at \gfr{90}.

\end{document}

Give \strange a better name. ;-)

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[Tex/LaTex] Typesetting unit-less numbers and number-less units

To typeset units without numbers, you can use \si{<unit>} (note the lower case).

The mathematically correct way to typeset ranges of values with units is to include the unit with each of the numbers. This is what the command \SIrange{<lower>}{<upper>} does. If you don't want to repeat the units, you can set [range-units = single].

Note that the most common units can be accessed using abbreviations (like \km for \kilo\metre).

\documentclass{article}
\usepackage{siunitx}

\begin{document}
The bird can fly \SIrange{40}{50}{\km\per\hour}.

The bird can fly \SIrange[range-units=single]{40}{50}{\km\per\hour}.

The data table above uses \si{\kg}.
\end{document}

[Tex/LaTex] Why use a package to typeset units

I came to this question thinking "yeah! Why?" but upon reading the currently extant comments and answer I have already changed my tune and am now tending the other way. What I realized, thinking about it and about my small interactions with this package, is that it provides much the same service within LaTeX as LaTeX (or even just TeX itself) provides for writing as a whole. To understand that point, consider the alternatives in communicating some math in writing via a computer:

Write it phonetically, as it were. Words are words, of course, but Greek letters are spelled out, or perhaps drawn in some ad-hoc ASCII art, and more complicated formulas are hacked together in an unspecified manner that may or may not be clear from context.
Write it in TeX, in which Greek letters are spelled out in macros, more complicated formulas are hacked together in some possibly awful manner...and then the result is "compiled" into a document making it all look like you had in mind, so no harm done if your source was a little more schematic than you'd have liked.

The siunitx package does exactly this, but instead of math formulas, it does SI-style units. Sure, one could write the same symbols that normally appear in such units as kg or s$^{-1}$, but that can go wrong visually very easily depending on if the unit appears in math mode or not (just imagine how that affects the latter!), or if several units become crammed together, or (egreg's quite valid observation) broken across a line. Then you may decide that instead of s$^{-1}$ you really want /s for the unit of hertz, necessitating a global change of notation.

These are all the kinds of problems that are handled in TeX by defining macros containing your preferred styles for \kilogram and \hertz and so on. The siunitx just organizes the whole project of defining these macros and their relationships to each other, and gives a lot of aesthetic options on top of it.

Basically, it boils down to "Why would anyone want to program their document in the first place?", to which the answer is "It's easier to write well-structured documents that way."

Best Answer

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[Tex/LaTex] Typesetting unit-less numbers and number-less units

[Tex/LaTex] Why use a package to typeset units

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