Rules & Regs: Part G of Form & Style Manual

The Return of Part G

 Rules & Regs columns from September/October 2010 and July/August 2012 each tackled various sections of Part G, Standards Style Manual, of the Form and Style for ASTM Standards. However, Part G is so packed with information that we still haven't covered everything. Here's a final look at Part G, primarily focusing on the section on proper use of numerals.

Numerals are obviously an enormously important part of nearly any standard, so it is important to express them properly. Section G18 of Form and Style provides rules that will help standards writers to be consistent in their use of numerals. Here is a rundown of G18.

G18.1 begins the Numerals style section with a very basic rule: all figures and tables should be designated by arabic numerals, for example, Fig. 3 and Table 6.

G18.2 notes that numbers from one to twelve should generally be spelled out, although there are some exceptions to this rule:

  • Use numerals when the quantity is partly fractional, such as 1.15 or 1 1/2.
  • Use numerals when followed by an expression having a standard unit symbol. Examples would be 25 mm, 45 kg or 9%.

G18.2.3 explains that the use of numerals is optional in cases in which the standard abbreviation or unit symbol of the expression following the number is not used, or if the expression has an abbreviation, such as year or ton. There are some exceptions to this rule:

  • In statements containing two or more numbers, one of which is greater than 12, all numbers should be expressed as numerals: " "2 tests and 16 weighings".
  • In a series of connected numerical statements implying precision, use numerals: "5 months, 3 days".
  • Use numerals after such abbreviations as "Vol." for volume and "Fig." for figure.

Numerals should be used for all numbers exceeding 12, with the following exceptions:

  • Do not begin a sentence with a numeral. An example of correct style: "One gram is usually sufficient."
  • Round numbers used in an indefinite sense, such as "a hundred meters or so," should be spelled out.
  • When two separate numbers are used back-to-back in a sentence, one of the numbers should be spelled out (fifteen 25-mm rods).
  • Place a zero before the decimal point in decimal numbers having no units, i.e., 0.65 mm, not .65 mm.

G18.4 notes that, when using a number of more than four figures, spaces should be used rather than commas in text, illustrations and tables. For example, 1 234 567. In the case of a four-figure number, no space or comma should be used ("1234") except in tables when the number occurs in a column containing number of more than four figures.

Other sections of G18 that may answer occasional style questions include the following:

  • G7 presents basic information on the use of chemical formulas in standards.
  • G10 addresses the use of dictionaries and other reference materials.
  • G19 details percent versus percentage points.
  • G23 describes the use of the words sample and specimen.


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