Measurement
Base quantity Base unit Symbol Current SI constants New SI constants ( proposed )
time second s hyperfine splitting in caesium-133 same as current SI
length metre m length of speed of light in vacuum , c same as current SI
mass kilogram kg mass of International Prototype Kilogram ( IPK ) Planck 's constant , h
electric current ampere A permeability of free space , permittivity of free space charge of the electron , e
temperature kelvin K triple point of water , absolute zero Boltzmann 's constant , k
amount of substance mole mol molar mass of Carbon -12 Avogadro constant N A
luminous intensity candela cd luminous efficacy of a 540 THz source same as current SI
Units and systems -- International System of Units
The International System of Units ( abbreviated as SI from the French language name Système International d'Unités ) is the modern revision of the metric system . It is the world 's most widely used system of units , both in everyday commerce and in science . The SI was developed in 1960 from the metre-kilogram-second ( MKS ) system , rather than the centimetre-gram-second ( CGS ) system , which , in turn , had many variants . During its development the SI also introduced several newly named units that were previously not a part of the metric system . The original SI units for the seven basic physical quantities were : [ 8 ]
Measurement is the assignment of a number to a characteristic of an object or event, which can be compared with other objects or events. The scope and application of measurement are dependent on the context and discipline. In the natural sciences and engineering, measurements do not apply to nominal properties of objects or events, which is consistent with the guidelines of the International vocabulary of metrology published by the International Bureau of Weights and Measures. However, in other fields such as statistics as well as the social and behavioral sciences, measurements can have multiple levels, which would include nominal, ordinal, interval and ratio scales. Measurement is a cornerstone of trade, science, technology, and quantitative research in many disciplines. Historically, many measurement systems existed for the varied fields of human existence to facilitate comparisons in these fields. Often these were achieved by local agreements between trading partners or collaborators. Since the 18th century, developments progressed towards unifying, widely accepted standards that resulted in the modern International System of Units (SI). This system reduces all physical measurements to a mathematical combination of seven base units. The science of measurement is pursued in the field of metrology.