NOTE 1 – Some derived units in the International System of Units (SI) have special names, e.g. hertz for frequency and joule for energy, but others have compound names, e.g. metre per second for speed. Compounds including units with special names are also used, e.g. volt per metre for the electric field strength, and newton metre for torque. See in particular ISO 31 and ISO/IEC 80000.

NOTE 2 – Derived units can also be expressed by using multiples and submultiples. For example, the metre per second, symbol m/s, and the centimetre per second, symbol cm/s, are derived units of speed in the SI. The kilometre per hour, symbol km/h, is a unit of speed outside the SI but accepted for use with the SI, because the unit hour is accepted for use with the SI. The knot, equal to one nautical mile per hour, is a unit of speed outside the SI, that is used by special interest groups.