Typography and Capitalization
In general, variables, unknown quantities, and constants (eg, x, y, z, A, B, C) are set in italics, while units of measure (eg, kg, mL, s, m), symbols (including Greek characters [see 17.0, Greek Letters]), and numbers are set roman. Also, subscripts or superscripts used as modifiers are set roman:
Cin = clearance of inulin.
Arrays (A) and vectors (V) should be set boldface. Mathematical functions, such as sin, cos, ln, and log, are set roman.
For equations that are set off from the text, the words and letters should be set roman and the equation should be capitalized by the same rules that apply to titles (see 10.2, Capitalization, Titles and Headings):