How to use numbers  

• be consistent when deciding whether to use numerals or words to represent numbers
• use numerals in scientific papers or projects that use numbers often
• start sentences with words, not numerals

Instances when you always use numerals  

• with abbreviations and symbols
• with units of measurement
• in addresses
• in dates
• in decimals
• in page numbers
• time

Instances when you always use words  

• if the number begins a sentence
• if the number can be written in one or two words
• if a non-statistical number is used in a sentence with other statistical numbers
• time followed by o'clock or if telling time in quarters, halves, or hours

Dates and Time  

• use words for centuries
• use words or numerals for decades
• BC follows the year number
• AD comes before the year number
• could also use BCE or CE, both placed after the year

Inclusive Numbers  

• for three digit number ranges, give only the last two digits of the second number unless more are needed to prevent misunderstanding
• for a range of years, take out the first two digits of the second year if they're the same as the ones on the first year (1987-98)
• write out the year numbers in a range if the first two digits are different (1900-2001)
• don't abbreviate year numbers for years before AD 1 or 1 CE

Roman Numerals  

• use capitalized ones in outlines or after names of people
• use lowercase roman numerals when writing the page numbers for an introductory section