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There is no single definition of anabsolute scale. In statistics and measurement theory, it is simply a ratio scale in which the unit of measurement is fixed, and values are obtained by counting.[1] Another definition tells us it is the count of the elements in a set, with its natural origin being zero, the empty set.[citation needed] Some sources tell us that even time can be measured in an absolute scale, proving year zero is measured from the beginning of the universe.[2] Colloquially, theKelvin temperature scale, where absolute zero is the temperature at which molecular energy is at a minimum, and theRankine temperature scale are also referred to as absolute scales. In that case, an absolute scale is a system ofmeasurement that begins at a minimum, or zero point, and progresses in only one direction.[3]
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Absolute scales are used when precise values are needed in comparison to a natural, unchanging zero point. Measurements oflength,area andvolume are inherently absolute, although measurements of distance are often based on an arbitrary starting point. Measurements ofweight can be absolute, such asatomic weight, but more often they are measurements of the relationship between twomasses, while measurements ofspeed are relative to an arbitraryreference frame. (Unlike many other measurements without a known, absolute minimum, speed has a known maximum and can be measured from a purely relative scale.) Absolute scales can be used for measuring a variety of things, from the flatness of anoptical flat to neuroscientific tests.[4][5][6]