Numbers and Symbols
Dates
The IEEE Policies and Procedures (Jan. 2000) specify the following formats for dates:
- E-mail and formal correspondence: day, month, year—for example, 6 January 2004.
- Software applications: four-digit year, two-digit month, two-digit day—for example, 2004-01-06.
- Centuries: Use the symbol for ordinal numbers—for example, 20th century. Note: CMS spells out the century—for example, twentieth century.
- Decades: The abbreviation is '90s, not ‘90s. Transactions use the four-digit format: 1990s.
Numerals
Spell out integers one through nine and use numerals for 10 on, except in the following cases:
As a general rule, numerals should be used even for one through nine when the integer is coupled with a symbol or unit of measurement (2°, 3 V). By the same token, numerals should be used with percentages even for one through nine (a 5 percent drop; 3 percent responded; 3 to 6 percent). However, in nontechnical passages, numbers less than 10 used with common units, especially time units, may look better spelled out, as do numbers used with approximate measurements:
| the program ran in 8 minutes [exact measurement] |
but | a report from eight years ago said [nontechnical] |
| he lives eight miles down the road [nontechnical] |
| about eight or nine centimeters [approximate] |
Spell out a number at the beginning of a sentence or recast the sentence.
In general, for units of measure, spell out on first use and abbreviate thereafter.
When a sentence includes both an integer less than nine and an integer greater than nine to describe something in the same category, use numerals for consistency—for example, The network can have 4, 8, or 16 nodes.
A compound adjective consisting of a number and an abbreviation is hyphenated. For example, 24-Kbyte memory.
Numbers with four digits or more have commas: 1,000, 10,000. Exceptions include page numbers and dates (CMS 9.55). Precede decimal fractions with values of less than one with a zero to prevent the reader from overlooking the period: 0.1 (however, observe the exceptions listed in CMS 3.70 and 9.19). And remember, they're singular: 0.1 inch, not 0.1 inches.
Use an s to create plurals of numerals:
- the early 1920s
- in twos, threes, and zeros
- he had a collection of 386s and 486s
Fonts and computers are inconsistent in the treatment and availability of fraction symbols. For in-text fractions, therefore, full-size numerals with a slash are usually preferred: 1/2, not ½. In more complicated mathematical expressions set in MathType, built-up fractions are generally used: numerator over denominator, separated by a horizontal line. In mixed numerals, put a hyphen between the integer and the fraction:
- 8-1/2 inches wide
- 24-5/8-mile track
For further reference see CMS Chapter 9, especially the parts on scientific and technical usage.
Symbols and signs
Use symbols in text only when you are certain that readers are familiar with them.
Multiplication symbol: Use the multiplication sign "´" instead of "by" when numerals refer to dimensions: 3 ´ 5 cm box; 3 in. ´ 5 ft. board.
Spacing of characters for units of measurement and symbols: Abbreviations for units of measurement, even if one letter, are separated from the numeral by a space (3 V, 5 m, 14 mm). Actual symbols, as opposed to abbreviations for units, can be closed up, for example, 42°30' for 42 degrees, 30 minutes latitude.
Use sq. ft., not "ft^{2}."
Do not use abbreviations when the reference is indefinite or casual—say "several gigahertz" not "several GHz." However, where brevity is a key factor—for example, in new product write-ups and tables—use symbols liberally.
When defining variables in run-in text, use "is" rather than "="; for example, "where t is the temperature," not "where t = the temperature."
Use the word "percent" in text; use the % symbol only in figures and tables.
Telephone and fax numbers
The IEEE Policies and Procedures specify the following format for phone and fax numbers:
In North America: +1 area code xxx xxxx; for example, +1 714 821 8380
Outside North America: +country code city code xxx xxxx; for example, in Belgium, +32 3 770 2242