152 Expressing Temperatures and Numbers

Style manuals, professional societies, and journals specific to your field publish thorough guidelines about how to handle small matters of mechanics. For instance, Suggestions to Authors of the Reports of the United States Geological Survey addresses such issues as whether to use the chemical name or symbol in writing; the American Meteorological Society’s Authors’ Guide dictates how one should express time, time zone, day, month, and year in writing. Chase down such sources within your field for specifics on matters of mechanics.

Two especially noteworthy issues of mechanics that arise regularly in technical writing are how to handle temperature measurements and numbers. Some guidelines on these matters follow.

Referring to Temperature Measurements

Degree measures of temperature are normally expressed with the ° symbol rather than by the written word, with a space after the number but not between the symbol and the temperature scale:

The sample was heated to 80 °C.

Unlike the abbreviations for Fahrenheit and Celsius, the abbreviation for Kelvin (which refers to an absolute scale of temperature) is not preceded by the degree symbol (i.e., 12 K is correct).

Writing about Numbers

The rules for expressing numbers in technical writing are relatively simple and straightforward:

All important measured quantities—particularly those involving decimal points, dimensions, degrees, distances, weights, measures, and sums of money—should be expressed in numeral form (e.g., 1.3 seconds, $25,000, 2 amperes).
Unless they appear as part of a string of larger related numbers, counted numbers of ten or below should be written out.
If possible, a sentence should not begin with a number, but if it does the number should be written out.
Treat similar numbers in grammatically connected groups alike.

Following these rules, here are some examples of properly expressed numbers:

The depth to the water at the time of testing was 16.16 feet.

For this treatment, the steel was heated 18 different times.

Two dramatic changes followed: four samples exploded and thirteen lab technicians resigned.