## Decimals

Decimal numbers are a linear way to represent fractions based on multiples of 10. The decimal *0.45* represents the following fraction:

^{45}/100

See FRACTIONS.

The decimal point (period) is the mark dividing the whole number on the left from the decimal fraction on the right:

- 504.678

In some countries, writers use a comma for the decimal point:

- 504,678

**Use figures for all decimals and do not write the equivalent fractions:**- 4.5 (
*not*4^{5}/10) - 0.356 (
*not*^{356}/1000) - 0.5 (
*not*/10)^{5} - 0.4690 (
*not*/10,000)^{4690}

- 4.5 (
**If the decimal does not have a whole number, insert a zero before the decimal point:**- 0.578 (
*not*.578) - 0.2 (
*not*.2)

NOTE: This rule has a few exceptions, including:

- Colt .45
- A batting average of .345
- A probability of
*p*=.07

- 0.578 (
**Retain the zero after the decimal point or at the end of the decimal number only if the zero represents exact measurement (or a significant digit):**- 0.45
*or*0.450 - 28.303
*or*28.3030

NOTE: Also retain the final zero in a decimal if the zero results from the rounding of the decimal:

- 23.180
*for*23.1789 (*if the decimal number is supposed to be rounded to three digits in the decimal fraction)*

- 0.45
**Use spaces but not commas to separate groups of three digits in the decimal fraction.**In the metric system, the decimals may be broken into groups of three digits by inserting spaces:

- 56.321 677 90
- 707.004 766 321
*but*567.4572 (*not*567.457 2)

You can use commas to separate groups of three digits that appear in the whole number part of the decimal:

- 56,894.65
- 500,067.453 467

However, do not use commas to separate groups of three digits in the decimal fraction:

- 4.672 34 (
*not*4.672,34) - 2344.000 567 (
*not*2344.000,567)

See METRIC SYSTEM.

**In columns, line up the decimal points:**- 56
- 0.004
- 115.9
- 56.24445
- 0.6

NOTE: Whole numbers without decimals (e.g.,

*56*above) do not require a decimal point.**Do not begin a sentence with a decimal number:***this*- The timer interrupts the processor 14.73 times a second.
*not this*- 14.73 times a second, the timer interrupts the processor.

See NUMBERS.