TITLE: Is it an abuse of notation to omit the leading zero in a decimal less than 1?
QUESTION [11 upvotes]: Is it acceptable to write $.001$ rather than $0.001$ when using decimal notation?
Are there contexts in which omitting the leading zero is acceptable, and other situations in which it is not?

REPLY [11 votes]: Depends on your style guide.

MLA Style requires the zero, as does US GPO style.
APA Style uses the zero before the decimal point if and only if it's possible for the thing being measured to be greater than one.  So a child could be “0.99 m” tall, but a probability could be “.99”.
Wikipedia requires the zero except for sports statistics (e.g., Ty Cobb batted .366) and commonly-used terms (a .22 caliber gun).