Consider the following example.




\[ \frac{x}{\SI{4}{\m\per\degree}} \]




Why is the per-mode option set to symbol? Shouldn't it be fraction or am I missing something obvious?

1 Answer 1


See the difference bettween per-mode=fraction and per-mode=symbol.


\[ \frac{x}{\SI[per-mode=fraction]{4}{\m\per\degree}} \]
\[ \frac{x}{\SI[per-mode=symbol]{4}{\m\per\degree}} \]
\[ \textstyle \frac{x}{\SI[per-mode=symbol-or-fraction]{4}{\m\per\degree}} \]
\[ \displaystyle \frac{x}{\SI[per-mode=symbol-or-fraction]{4}{\m\per\degree}} \]
\[ \frac{x}{\SI[per-mode=symbol-or-fraction]{4}{\m\per\degree}} \]
\[ \frac{x}{\displaystyle\SI[per-mode=symbol-or-fraction]{4}{\m\per\degree}} \]

enter image description here

In fact, in the last two equations, \per should be printed as fraction, like the siunitx manual (bottom of p. 41) points out:

Setting per-mode to symbol-or-fraction will use the symbol setting for in line math, and the fraction setting when used in \displaystyle math.

There is probably a bug or an omission of some option.

  • 1
    How is it a bug? The denominator of a displaystyle fraction is in textstyle by default, just see the output of \frac{1}{\sum_{i=1}^{n}{a_i}}.
    – T. Verron
    Apr 29, 2013 at 5:30
  • @T.Verron Okay. I, as well, thought it was in \displaystyle math. Apr 29, 2013 at 5:49
  • 2
    I'd say this is a subtly that should probably go into the manual: @T.Verron is correct that \textstyle is active at the point of choice (and I'd say this looks 'best'), but that might not be obvious to most people.
    – Joseph Wright
    Apr 29, 2013 at 6:06
  • I edited my answer to add the \displaystyle in the denominator. As expected the visual result is not the same as using the per-mode=fraction.
    – cacamailg
    Apr 29, 2013 at 9:45

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