Some elements such as numbers, abbreviations, and symbols require special consideration in technical writing.

Numbers vs. Words

In most contexts other than technical writing, you may have been taught to use words for numbers below ten. However, in technical contexts, you use numbers, even ones below 10, in certain cases. In technical and scientific contexts, readers are vitally interested in numbers and statistical data, even if it’s a 2, a 5, or even a 0.

When to use Numbers

Use numbers when you have an exact, measured, or measurable amount. For example, in the following sentences, numbers indicate exact, measured amounts:

• The completed model should be 13 inches tall.
• Use all 5 screws to fasten each leg to the table.
• Our computer backup system uses 4 mm tape.
• The recipe calls for 2 cups of unbleached flour.

When to Use Words

Use words when the amount does not matter in terms of measurement. In the following examples, the amount does not relate to something that needs to be measured or exact; there might be any number of items in any of the examples:

• There are four key elements that define a successful technical description.
• This process involves five steps.
• Having three people involved in building the model will make step 7 easier to complete.
• There are six data types in this programming language.

Use words when a value occurs at the start of a sentence; don’t start a sentence with a number. However, if the number refers to an exact, measurable amount, it’s better to revise the sentence and use different first words so that you can use the number appropriately.

Conventions for Writing Numbers and Words

Apply the following conventions in technical communications:

• For decimal values less than 1, add a 0 before the decimal point: for example, .08 should be 0.08.
• Do not go back and forth between decimal values and fractions in one document; choose one or the other.
• For fractions, put a hyphen between the whole number and the fraction, like this: 5-1/4.
• For large amounts, use a combination of numbers and words, like this: 31 million, 44 billion
• Always use a number before the word “percent,” like this: Over 65 percent of the gross income goes toward staff salaries.

Abbreviations & Acronyms

Since technical writing should be as concise as possible, technical writers use abbreviations and acronyms freely. Abbreviations are shortened forms of words (e.g., medical personnel usually abbreviate the word “prescription” to “script”).  Acronyms are shortened forms of phrases, using the first letters of words in the phrase (e.g., World Health Organization = WHO). Abbreviations and acronyms often become standard shorthand for practitioners in a field.

Three usage rules apply to using abbreviations and acronyms:

1. If there’s any possible audience member who may not understand the abbreviation or acronym, or if audience members might interpret the short version differently based on their backgrounds, write out the whole word or phrase the first time you use it. Do not sacrifice clarity and precision for conciseness. Put the shorter form in parentheses immediately after the whole word or phrase like this: World Health Organization (WHO). After the initial definition, it’s OK to use the shorter form. The only time you do not need to define an abbreviation or acronym is when you’re very sure that your audience will understand and define the shorter version accurately, in the way you intend.
2. Abbreviations do not go up against numbers. Use a hyphen or space between a number and an abbreviation. For example, use this: 8-mm tape or 8 mm tape. Do not use this: 8mm tape.
3. Do not put a period after technical abbreviations (e.g., mm, kg). Use a period only after general abbreviations (e.g., i.e.).

Symbols

There are many symbols that may be used in technical communications. Remember, though, that it’s better to use fewer symbols than many.

Inches and Feet

The most common problem with symbols in instructions and descriptions has to do with inches and feet. In most cases, write out or abbreviate inches (in.) and feet (ft.) because the letters are easier to read than the marks, and offer less chance for misreading, especially if a reader is skimming the document. Note that using the whole word is preferable to the abbreviation.

The only time you can use symbols for inches ( ” ) and feet ( ‘ ) is if you’re writing about a building project and there are many, many instances in which you need to provide measurements. If you cite inch and foot measurements only a few times, use the word or abbreviation instead.

Percent ( % )

In the text of a technical document, you may write out the word “percent” after a number, or may use the % sign. However, use the % sign in tables or charts so that you’re presenting information in the most concise way.

Ampersand ( & )

Another symbol that you might encounter frequently is the ampersand (&). Use the ampersand symbol in company names only if the companies themselves do so, and use the ampersand symbol in titles or headings if you need to keep them condensed. However, avoid using the ampersand instead of the word “and” in your sentences; write out “and” in all sentences.

Temperature/Degrees

In technical settings, 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).