Are you working in science and need to report quantities based on the SI system?

When I rehearse presentations with my students or review their reports, I often notice that they need guidance in formatting and typesetting SI quantities properly. I must admit that my years in metrology have made me examine this more closely. I compiled this summary for quick reference and as a visual reminder.

The good thing is that there are just a few basic rules to follow, and you can master that field. The zeroth rule is to make it consistent in your documents. There is even a great document published by the #BIPM —the guardians of the SI units—on how to use units properly: 🌐https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf Chapter 5 talks about all the typesetting details. The good thing is that this chapter is quite short and gives you all the rules for typesetting in detail.

In brief:

• Depending on the geographic or language preferences, the decimal separator can be either 0.0 or 0,0.
• There is a space between the numeric value and the unit. The space denotes a multiplication symbol. In the best case, use a non-breaking space (Ctrl+Shift+Spacebar in Word, ~ in LaTeX) so that both parts stay together under all circumstances.
• The font of the SI-unit symbol is upright, not italic or bold. If you typeset equations in Word, you need to adjust that.

Don’ts:

• Do not alter the SI unit symbols. There can not be indices or subscripts.
• Don’t use non-standard unit symbols like 1 sec—it is 1 s—or plural forms like 10 mins—it is 10 min.
• Avoid non-SI units.
• There can not be a line break between the value and the unit. Use non-breaking spaces to keep it together.

Do’s:

• Check that there are no ambiguities. The letter m—, which can be either meter or the prefix milli- —, requires attention. Use a (small) space or a multiplication dot to separate units.
• Structure the unit symbols with brackets, especially if you use the oblique stroke (/) for division. Alternatively, use the exponential representation.
• Percent (10 %) and degree Celcius (10 °C) use the same rules as all other SI units and require a space. For angular degrees, there is no space (360°).
• Never put any additions to SI unit symbols. (Never write Vpp)
• There is no hyphen in combination with the unit symbols. Use the spelled unit name in combination with a hyphen.

In LaTeX, you can use the siunitx package, which will handle most of the typesetting stuff for you. 🌐https://ctan.org/pkg/siunitx?lang=en