![]() The same value of a speed v = d x/d t of a particle might be given by either of the expressions v = 25 m/s = 90 km/h, where 25 is the numerical value of the speed in the unit metres per second, and 90 is the numerical value of the speed in the unit kilometres per hour. Thus the value of a particular quantity is independent of the choice of unit, although the numerical value will be different for different units. The numerical value of a quantity depends on the choice of unit. The value of a quantity is expressed as the product of a number and a unit, and the number multiplying the unit is the numerical value of the quantity expressed in that unit. Note that symbols for quantities are only recommendations, in contrast to symbols for units whose style and form is mandatory. ![]() Symbols for quantities are generally single letters set in an italic font, although they may be qualified by further information in subscripts or superscripts or in brackets. Non-SI units associated with the CGS system of units.Non-SI units whose values in SI units must be obtained experimentally.Non-SI units accepted for use with the International System of Units.Examples of SI coherent derived units whose names and symbols include SI coherent derived units with special names and symbols.Coherent derived units in the SI with special names and symbols.Examples of coherent derived units in the SI expressed in terms of base units.
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