# Use of math mode with SIstyle

When using the SIstyle package, I noticed that numbers inside \SI{}{} and \num{} appear in a slightly different style than inside .

• Do the \SI{}{} and \num{} commands come with math mode already?
• Should I place math mode around this? E.g. $\SI{}{}$ and $\num{}$.
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Answers to your questions are on p. 4 of the sistyle user guide: "The numbers and units are set inside a math environment with an upright font. When the \SI command is used in normal text or inside inline maths, it follows the surrounding fonts. Display maths on the other hand will follow the active math fonts." Just in case you're not aware of this, the sistyle package ceased development and maintenance (other than simple bug fixes) several years ago. You may want to switch to using the siunitx package instead. –  Mico Jan 23 '12 at 2:51
I looked at the documentation for siunitx, but could not find many of the units I need (e.g. "Mach", "ton", "pound", "light year", "liter", "inch", "Light year"), so I thought perhaps sistyle would be better. –  Village Jan 23 '12 at 2:57
@Village: siunitx is quite strict with what units are included by defaults (almost exclusively "proper" SI units). Litres/liters are included as \litre (yielding l) and \liter (yielding L), tons are \tonne. The other units can be defined really easily using \DeclareSIUnit\mach{Ma}, \DeclareSIUnit\pound{lbs}, \DeclareSIUnit\inch{in}, and \DeclareSIUnit\lightyear{ly}. I would definitely recommend going with siunitx, especially for the great number printing and tabular alignment features. –  Jake Jan 23 '12 at 3:11
Check out section 4.5 of the siunitx manual and the \DeclareSIUnit command for guidance on creating one's own (highly non-SI!) units. E.g., \DeclareSIUnit\lightyear{ly} should work for you, right? siunitx recognizes \tonne, by the way (though not \ton). –  Mico Jan 23 '12 at 3:12
'tonne' is a metric unit and is in the BIPM docs (bipm.org/en/si/si_brochure/chapter4/table6.html). 'ton' is the name for two imperial units: the long ton (2240 lb) and the short ton (2000 lb). –  Joseph Wright Jan 23 '12 at 8:41

SIstyle follows the local environment font definition. If your text and math fonts (mathrm) are different, it will give different output.
I am not doing any further development work (just maintenace) on SIstyle and everthing has moved over to siunitx where Joseph Wright is doing a fantastic job. I would recommend to change to siunitx
Okay, I will switch to siunitx. –  Village Jan 23 '12 at 8:01