In technical and statistical writing and with SI/metric units, decimals are preferred to fractions. Normally, no number should begin or end with a decimal point. A zero is written before the decimal point of numbers smaller than 1, while in whole numbers the decimal point should either be dropped or be followed by a zero:
See also 5.16 Market quotations.
Zeros may be used to indicate the number of decimal places to which a value is significant: 0.60 implies significance to two decimal places, 0.600 to three.
In many countries the decimal marker is the comma, not the period. In Canada, however, the period is the generally used decimal marker in English-language texts.
The Canadian Metric Practice Guide (CAN/CSA-Z234.1-89) of the Canadian Standards Association specifies that groups of three numerals (triads) shall be separated by a space, except in the case of monetary values. It advises against the use of commas as separators. Although both commas and spaces are still widely used in Canada, The Canadian Style recommends that, except in financial documents, a space be used instead of a comma. Such a space is also to be inserted after groups of three digits to the right of a decimal point. Note that numbers of four digits only (on either side of the decimal marker) need not be so spaced unless used in combination with other numbers of more than four digits. The following examples illustrate the correct use of the space to separate triads of numbers:
|5005 or 5 005||5.0005 or 5.000 5|
|50 005||5.000 05|
|500 005||5.000 005|
|500 005 000||5.000 005 000|
Omit the space in pagination, inclusive numbers, addresses, numbering of verse, telephone numbers, library numbers, serial numbers and the like.
Sums of money are usually expressed in numerals, except when they refer to round or indefinite amounts or are used in a formal or legal context:
Use the following forms:
The abbreviations B for billion, M for million and K for thousand are often encountered, especially in newspaper headlines. Avoid them in formal writing. Note that there is no space between the numeral and the letter:
When dollar amounts are used with SI symbols, the following forms are required:
Place the dollar sign before the numeral in question.
For representation of dollar amounts in Canadian and other currencies, see 5.26 Other considerations.
Clarity should be the primary consideration when communicating numerical information. Present it in such a way that it will be readily grasped by the reader. When writing for non-Canadians, make sure you are aware of the conventions used in the target country. Europeans, for example, who are steeped in the metric system, do not confine themselves as we usually do to multiples of 1000. They will more naturally write 3 dL (decilitres) than 300 mL or 0.3 L. Material written for the European market should conform to this practice.
Remember, too, that in Europe—and in Quebec—1,500 means "one and a half," and 1.500 means "fifteen hundred." The British "billion" is the equivalent of the American "trillion," while a British "trillion" is a million million million. In certain circumstances it may be advisable to write a thousand million or 109 or giga- instead of billion, and a million million or 1012 or tera- instead of trillion, to avoid the risk of misinterpretation. For similar reasons, the abbreviation ppb (parts per billion) should not be used. Rewrite 100 ppb as 0.1 ppm.
Dollar amounts in different currencies should be distinguished from one another by some easily understood marker. A reference to $20 will be ambiguous to a non-Canadian reader and may be taken to refer to American or some other currency. No single system is universally accepted, but the following is the one used by the Department of Finance and the International Monetary Fund:
If greater clarity is required, the abbreviations CAN and AUS may be used. Note that CAD and AUD are also becoming increasingly current.
Where the reader may be in doubt as to which conventions should be followed for writing numerical expressions, the safest course is to adhere to international conventions (see 5.09 Decimal fractions, notes 1 and 2).
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