A previous article explained how you can express quantities such as speed, concentration, or dose in your manuscript. Apart from these, expressions of rates – milligrams per litre, kilometres per hour, and tonnes per hectare, for example – are common in research papers. Rates can be voiced in several ways: the three examples above can be rendered as mg/L, km/h, and t/ha or even as mg L–1, km h–1, and t ha–1. Which method should you use? The choice depends very first on the target journal: examine a latest issue of the target journal and go after the method used by that journal. Negative exponents are typically seen in journals, never in magazines. Expressions using ‘per’ are common in most non-technical writing. Some trade journals use yet another alternative: kmph, for example, instead of kilometres per hour, but that is not in line with the style prescribed by Comite International des Poids et Mesures, the CIPM (known in English as the International Committee for Weights and Measures). Albeit all the methods are correct and acceptable, each has its petite points of style, and this article explains some points of style related to the method of using negative exponents.
- Recall to use the minus sign (or the en dash); never use the hyphen.
- If the font provides true superscript characters, use them. Most fonts provide superscript Two and superscript Trio (inserted, respectively, by the combinations alt + 0178 and alt + 0179) and some provide all the numerals from 1 to 9 both as superscripts and subscripts. You can lightly see the difference for yourself. Type the numeral Two, for example, select it, and make it a superscript. Next to that, insert the true superscript character (alt + 0178). The true superscript is as black as the rest of the characters whereas the formatted superscript Two looks lighter.
- Use the non-breaking space (alt + 0160) for the gap inbetween the two symbols (inbetween km and h–1 for example). The asterisk and the middle dot (·, alt + 0183) are also seen; if the target journal uses either of these, use it.
I hope these tips help you in your writing. You can also read these articles for more guidance:
Converting non-SI units to SI units: psi, mesh number, and quintals
Tips on using major headings, subheadings, minor headings in research papers
How to include author-year citations into the text of research papers