the recommended symbol for the physical quantity "mass" is m, and the recommended symbol for the quantity "electric charge" is Q.

Physical quantities are normally typeset in italics.Purely numerical quantities, even those denoted by letters, are usually printed in roman (upright) type, though sometimes in italics. Symbols for elementary functions (circular trigonometric, hyperbolic, logarithmic etc.), changes in a quantity like ? in ?y or operators like d in dx, are also recommended to be printed in roman type.

Examples:
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