This section offers concrete advice about some of the mechanics of style for presenting equations. For specific rules about such details as punctuation, spacing, or the flushing of elements, the best idea is to check out a journal or textbook in your field and learn by example.

In the absence of any rules about how equations are presented in a particular class, follow these best practices when using equations:

• Set off and center equations on their own separate lines of text if the equations are long, contain more than one or two symbols that must be identified, or contain expressions with numerators and denominators that fall on different lines.
• When you center an equation, skip a line above and below it, and skip an extra line or two if the equation includes any symbols of more than letter height. Make the equation easy to find and easy to read.
• When appropriate, define any symbols that you use.
• If possible, do not let an equation spill from one page to another.
• Equations are not always numbered, especially if only a handful occur in a paper. However, if you need to refer back to equations already introduced in the text, you should number all equations in sequence. Do this by identifying the number of the equation in parentheses at the right-hand margin of the line on which the equation appears. Then you can readily refer back to it with a phrase such as “Equation 3 describes a contrasting relationship.”
• When numbering an equation, be sure the number is set far enough away from it that it does not seem to be a member of the equation.