Numbers: Documenting Numerical Information

The prior article in this newsletter dealt with documenting complex topics at the right level of detail. This article is about documenting numerical information.

Numbers may be needed in a document to represent instrument readings, calculated values, or control settings. Quantities are most often accompanied by a unit of measure and should be expressed as numerals. In general, use numbers (0, 1, 2) instead of spelling them as words (zero, one, two). However, spell out the number if it has no unit of measure, e.g., “use one of the following”. Or, if it may cause confusion, e.g., “use one 9 volt battery” rather than “use 1 9 volt battery”.

If applicable, specify the unit of measure with the numbers. Use the same units of measure as indicated on the equipment, for example, degrees Fahrenheit. Specify numbers only to the precision (exactness) available on the equipment or data source. Use ranges to specify acceptable limits of operation. For example, 10 – 20 is a range.

Do not express it as an error band (15±5). Avoid asking users to make a calculation. If it is necessary, provide them with a calculation aid in the document to simplify the formula and reduce errors.