FUNDAMENTAL DIMENSIONSUnit SystemsCP-01 Page 2Rev. 0TimeTime is the duration between two instants. The measurement of time is described inunits of seconds, minutes, or hours.UnitsA number alone is not sufficient to describe a physical quantity. For example, to say that "apipe must be 4 long to fit" has no meaning unless a unit of measurement for length is alsospecified. By adding units to the number, it becomes clear, "a pipe must be 4 feet long to fit."The unit defines the magnitude of a measurement. If we have a measurement of length, theunit used to describe the length could be a foot or yard, each of which describes a differentmagnitude of length. The importance of specifying the units of a measurement for a numberused to describe a physical quantity is doubly emphasized when it is noted that the samephysical quantity may be measured using a variety of different units. For example, length maybe measured in meters, inches, miles, furlongs, fathoms, kilometers, or a variety of other units.Units of measurement have been established for use with each of the fundamental dimensionsmentioned previously. The following section describes the unit systems in use today andprovides examples of units that are used in each system.UnitSystemsThere are two unit systems in use at the present time, English units and International Systemof Units (SI).In the United States, the English system is currently used. This system consists of various unitsfor each of the fundamental dimensions or measurements. These units are shown in Table 1.