UnitsPut a space between the number and the unit (5 km, 200 g). The exceptions are degrees of temperature or latitude (N 49°15′48.14″, W 123°9′43.34″, 5°C, 5°F), percent signs (5%), and prime signs (6′2″). Some styles allow a space before the degree symbol in temperatures (5 °C). (The symbols for minutes and seconds in latitude and longitude or feet and inches are the prime and double prime. See “Special characters” below.)
Capitalization: the abbreviation for litre (L) and millilitre (mL) may use a capital L to distinguish it from a 1 (one).
When two quantities go together, repeat the symbol only if there is no space between the number and symbol (CMOS 9.17): 3%–5%, 4–5 km, 6″ × 9″, and 39°C–40°C.
NumbersYou’re likely to have a lot of numbers in your text. Here are a few guidelines.
- Use en dashes instead of hyphens in ranges of numbers (8–10). The en dash is slightly longer than a hyphen.
- When writing in English, use a period (not a comma) for the decimal point, and commas (not periods) to separate groups of three digits. Some styles use spaces to separate groups of three digits. It is also permissible to omit the comma in a four-digit number. Be consistent.
- Numerals versus spelled-out numbers. In the absence of other instructions, a safe policy is:
- Spell out single-digit numbers and use numerals for all others: “all three study areas,” “in 2.3% of the samples.”
- If a number is given with a unit, use the numeral even if it’s a single-digit number: “each test tube contained 2 mL of solution” (not “two mL”).
- If you start a sentence with a number, it should be spelled out: “Twenty-seven of the volcanoes ...” But if the number takes a unit (“Two mL of solution was put in each test tube”), then I recommend you rewrite the sentence.
Spacing with mathematical symbols
- There should be no space between the number and sign: “−1°C,” “1000× magnification.”
- There should be spaces around the operator in a binary operator “p < 0.005.”
Some codes for special characters
- En dash: Unicode U+2013, HTML –, option-hyphen on a Mac
- Degree symbol: Unicode U+00B0, HTML °
- Primes and double primes for latitude and longitude: Unicode U+2032 and U+2033, HTML ′ and ″
- Minus sign: Unicode U+2212, HTML −
- Multiplication sign: Unicode U+00D7, HTML ×
- How to write typographers’ quotes (smart quotes) in HTML
Scientific names of organismsSee writing scientific names of organisms.
Spacing between sentencesUnless you are writing for a journal that specifies otherwise, use only one space after a period or colon. It will save your publisher from having to remove the extra spaces, and they’ll like you better if you don’t make them do that. If you’re writing for the web or working on a thesis, leave the extra spaces out; they’ll just look awkward and unprofessional.
Text alignmentI suggest aligning your text on the left instead of justifying it. Publishers usually request left alignment in manuscript submissions, and the consistent spacing between words makes it easier to read and edit.
- Chicago Manual of Style, 16th edition. There’s a free 30-day subscription available. Subjects to check out: guidelines for hyphenation, setting mathematics in type, extensive notes on citations and references.
- Butcher’s Copy-Editing has 43 pages on science and mathematics. Chapter 13: “Science and Mathematics books” has sections on nomenclature, units, astronomy, biology, chemistry, computing, geology, medicine, and references. There is also material on indexes, special characters and mathematical symbols, and how to produce illustrations that are suitable for publication.
- New Hart’s Rules also has a section on scientific naming and style. (This book is much cheaper than Butcher’s, so if you only want to buy one style guide, that’s worth keeping in mind.)
- Two good articles on preparing your paper and the submission process: “How do I write a scientific paper?” and “How do I submit a paper to a scientific journal?” This last article is by Maxine Clarke, executive editor of Nature.
- International List of Periodical Title Word Abbreviations
- Subtleties of Scientific Style by Matthew Stevens has some very good suggestions for making academic writing more clear. His book is available for download as a PDF file.