[Tex/LaTex] Which measurement units should one use in LaTeX

best practicesunit-of-measure

There are various measurement units that one can use (such as pt, mm, in, em, ex etc.) for specifying lengths and heights. For font-based units (em and ex) the actual spacing will vary slightly depending on the font. For the other types of units the spacing is fixed at the given measurement.

Is it better to prefer some of these units over others in certain situations? For example, is the "em" unit better than a fixed measurement when specifying lengths for indenting text eg. when setting xleftmargin, and xrightmargin in the listings package. When would you use the "ex" unit for specifying heights? I imagine fixed units should always be used when setting page margins.

So, I guess what I am asking is, what are the guidelines for deciding which measurement units to use?

Best Answer

There are no hard-and-fast rules, but here's a short list of guidelines:

"1em" can be considered a horizontal length and "1ex" a vertical one, so use them accordingly but mix and match as you need (they are horizontal and vertical arbitrarily, but usually you hear people talk about "1em" is the width of an "m" — usually false — and "1ex" is the height of an "x" — usually true). I usually consider 1em to be about the same size as the font size in points.
em and ex are relative lengths, so they're better for designing around text; like you say, an indent of 2em will work whether the fontsize is 9pt or 12pt.
Things that are of fixed size (such as the page size) should be defined with fixed units, of course.
When things should be relative, it will often make more sense to define them in terms of the page design. For example, width=0.5\linewidth might make more sense than width=5cm for a figure.
Watch out for the pt unit! In TeX, 1pt is 1/72.27in, whereas the more common "PostScript point" used by most other software is 1/72in which in TeX is 1bp. If you're dealing with other programs and need your lengths exact, use bp or use standard cm or in measurements.
Remember that TeX uses fixed point arithmetic, so there are precision problems when you hit around five significant figures. E.g.,
```
  \newlength\x
  \x=1in
  \showthe\x
```
gives
```
  > 72.26999pt.
```

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[Tex/LaTex] When should one use \begingroup instead of \bgroup

\bgroup is a synonym for {, which is defined in Plain TeX using \let\bgroup={.

It interacts with TeX's "digestive system" in hairy ways: {s and \bgroups start the same sort of groups, called simple groups, and each can be terminated with either }s or \egroups, since they are the same. But when the TeX digestive system encounters them, they are of different catcodes, so commands that look ahead, e.g., in LaTeX with \section\bgroup Title}, can break this matching.

\begingroup is different. It is a TeX primitive, and it matches a different sort of group that TeX accounts for separately, called "semi-simple groups" (a Knuth joke, I assume). Thus a \begingroup must be terminated by an \endgroup, not a }, and vice versa for \endgroup.

I generally avoid \bgroup, and use \begingroup, but \bgroup could be useful if you are messing about with a nested token list.

[Tex/LaTex] Which unit of measurement for textwidth

In theory you can use any supported unit. What is important, however, is that in case you have only normal paragraph text that this text properly fills the page (meaning that it doesn't have to be stretched apart to fill the page body as there may be nothing to stretch). It is therefore useful to define the \textheight as a function of \baselineskip and \topskip.

\baselineskip  is the distance from one baseline to the next in a paragraph
\topskip       is the distance from the top of the page area to the baseline of 
               the first line (if the page starts with a line)

For example in the standard book class (without an option like 11pt) the \baselineskipis 12pt and the \topskip is 10pt so a page with 40 lines should be 478pt. Of course you could achieve the same by giving the equivalent of that value in cm or mm but given that baselineskips are traditionally specified in points ...

If you use a value that isn't a multiple of baselineskip + topskip you may find to get "underfull" warnings, because TeX then tries to stretch pages to fill all space (that would happen in the bookclass, for example, as this class uses the setting `\flushbottom).

However, a better solution might be to use the package geometry that does a lot of work like this for you when setting up the page area. Have a look at its documentation.

Best Answer

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