Spell out the whole numbers one through nine. Write other numbers using digits. (In humanistic works, you may choose to spell out all whole numbers less than 100.) Treat ordinals in the same way as cardinal numbers.
Always spell out numbers at the start of a sentence. Reword sentences to avoid spelling out large numbers.
Spell out round numbers and approximations.
Round numbers and approximations greater than one million may be expressed with a combination of words and digits. Exact figures should be expressed using digits.
Use digits for numbers used as nouns, exact measurements, decimal fractions, and percentages.
The International System of units (SI units), commonly known as the metric system, requires that digits be used with abbreviated units, and spelledout numbers are used with spelledout units.
Related numbers should be expressed consistently.
When two numbers are adjacent, spell out one of them. Usually, the one with fewer letters is spelled out.

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