Units of measure
Use only units of the International System of Units (SI) to express the values of quantities. Equivalent values in nonmetric units may be given in parentheses following SI values in cases where safety may be an issue, or when they’re used in a product’s name.
International authority: Bureau International des Poids et Mesures (BIPM), https://www.bipm.org
Standard: BIPM SI Brochure. United States interpretation is available from the Department of Commerce at https://www.nist.gov/pml/pubs.
Usage: Quantities are always expressed with a unit symbol. Use a nonbreaking space (Option-Space bar) between the quantity and its symbol. Unit symbols are unaltered in the plural, and are never hyphenated, even when they’re used as an adjective. Unit symbols aren’t followed by a period unless they appear at the end of a sentence. Don’t imply more precision than is reasonable in choosing a unit symbol.
The Apple HDMI to HDMI Cable is 1.8 m long.
The 13-inch MacBook Air computer weighs 1.35 kg.
The iPad mini 4 Wi-Fi models weigh 298.8 g (0.65 lb.).
The iMac computer has a 1.6 GHz, 2.8 GHz, or 3.1 GHz processor.