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# International System of Units

The International System of Units (SI, abbreviated from the French Système international (d'unités)) is the modern form of the metric system, and is the most widely used system of measurement. 

## Absorbed dose

Absorbed dose is a measure of the energy deposited in a medium by ionizing radiation.

## Acceleration

In physics, acceleration is the rate of change of velocity of an object with respect to time.

## American English

American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States.

## Amount of substance

Amount of substance (symbol for the quantity is 'n') is a standard-defined quantity that measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles.

## Ampere

The ampere (symbol: A), often shortened to "amp",SI supports only the use of symbols and deprecates the use of abbreviations for units.

## Anders Celsius

Anders Celsius (27 November 170125 April 1744) was a Swedish astronomer, physicist and mathematician.

## Angle

In plane geometry, an angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle.

## Archives Nationales (France)

The Archives Nationales (Archives nationales de France), also known as the French Archives or the National Archives, preserve France's official archives apart from the archives of the Ministry of Defence and the Ministry of Foreign Affairs, as these two ministries have their own archive services, the Defence Historical Service (Service historique de la défense) and the Diplomatic Archives (Archives diplomatiques) respectively.

## Area

Area is the quantity that expresses the extent of a two-dimensional figure or shape, or planar lamina, in the plane.

## Astronomical unit

The astronomical unit (symbol: au, ua, or AU) is a unit of length, roughly the distance from Earth to the Sun.

## Atmospheric pressure

Atmospheric pressure, sometimes also called barometric pressure, is the pressure within the atmosphere of Earth (or that of another planet).

## Atom

An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element.

In chemistry and physics, the Avogadro constant (named after scientist Amedeo Avogadro) is the number of constituent particles, usually atoms or molecules, that are contained in the amount of substance given by one mole.

## Bar (unit)

The bar is a metric unit of pressure, but is not approved as part of the International System of Units (SI).

## Barn (unit)

A barn (symbol: b) is a unit of area equal to 10−28 m2 (100 fm2).

## Barye

The barye (symbol: Ba), or sometimes barad, barrie, bary, baryd, baryed, or barie, is the centimetre–gram–second (CGS) unit of pressure.

## Becquerel

The becquerel (symbol: Bq) is the SI derived unit of radioactivity.

## Blaise Pascal

Blaise Pascal (19 June 1623 – 19 August 1662) was a French mathematician, physicist, inventor, writer and Catholic theologian.

## Blood pressure

Blood pressure (BP) is the pressure of circulating blood on the walls of blood vessels.

## Boiling point

The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.

## Boltzmann constant

The Boltzmann constant, which is named after Ludwig Boltzmann, is a physical constant relating the average kinetic energy of particles in a gas with the temperature of the gas.

## British English

British English is the standard dialect of English language as spoken and written in the United Kingdom.

## British Science Association

The British Science Association (BSA) is a charity and learned society founded in 1831 to aid in the promotion and development of science.

## Cambridge University Press

Cambridge University Press (CUP) is the publishing business of the University of Cambridge.

## Candela

The candela (or; symbol: cd) is the base unit of luminous intensity in the International System of Units (SI); that is, luminous power per unit solid angle emitted by a point light source in a particular direction.

## Capacitance

Capacitance is the ratio of the change in an electric charge in a system to the corresponding change in its electric potential.

## Carbon-12

Carbon-12 is the more abundant of the two stable isotopes of carbon (Carbon-13 being the other), amounting to 98.93% of the element carbon; its abundance is due to the triple-alpha process by which it is created in stars.

## Carcel lamp

The Carcel lamp was an efficient lighting device used in the nineteenth century for domestic purposes and in France as the standard measure for illumination.

## Carl Friedrich Gauss

Johann Carl Friedrich Gauss (Gauß; Carolus Fridericus Gauss; 30 April 177723 February 1855) was a German mathematician and physicist who made significant contributions to many fields, including algebra, analysis, astronomy, differential geometry, electrostatics, geodesy, geophysics, magnetic fields, matrix theory, mechanics, number theory, optics and statistics.

## Catalysis

Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalysthttp://goldbook.iupac.org/C00876.html, which is not consumed in the catalyzed reaction and can continue to act repeatedly.

## Celsius

The Celsius scale, previously known as the centigrade scale, is a temperature scale used by the International System of Units (SI).

## Centimetre–gram–second system of units

The centimetre–gram–second system of units (abbreviated CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time.

## Coherence (units of measurement)

A coherent system of units is based on a system of quantities in such a way that the equations between the numerical values expressed in coherent units have exactly the same form, including numerical factors, as the corresponding equations between the quantities.

## Comma

The comma is a punctuation mark that appears in several variants in different languages.

## Commission on Isotopic Abundances and Atomic Weights

The Commission on Isotopic Abundances and Atomic Weights (CIAAW) is an international scientific committee of the International Union of Pure and Applied Chemistry (IUPAC) under its Division of Inorganic Chemistry.

## Conventional electrical unit

A conventional electrical unit (or conventional unit where there is no risk of ambiguity) is a unit of measurement in the field of electricity which is based on the so-called "conventional values" of the Josephson constant and the von Klitzing constant agreed by the International Committee for Weights and Measures (CIPM) in 1988.

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## Coulomb

The coulomb (symbol: C) is the International System of Units (SI) unit of electric charge.

## Country

A country is a region that is identified as a distinct national entity in political geography.

## Curie

The curie (symbol Ci) is a non-SI unit of radioactivity originally defined in 1910.

## Darcy (unit)

A darcy (or darcy unit) and millidarcy (md or mD) are units of permeability, named after Henry Darcy.

## Day

A day, a unit of time, is approximately the period of time during which the Earth completes one rotation with respect to the Sun (solar day).

## Decibel

The decibel (symbol: dB) is a unit of measurement used to express the ratio of one value of a physical property to another on a logarithmic scale.

## Decimal separator

A decimal separator is a symbol used to separate the integer part from the fractional part of a number written in decimal form.

## Degree (angle)

A degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by ° (the degree symbol), is a measurement of a plane angle, defined so that a full rotation is 360 degrees.

## Dimensional analysis

In engineering and science, dimensional analysis is the analysis of the relationships between different physical quantities by identifying their base quantities (such as length, mass, time, and electric charge) and units of measure (such as miles vs. kilometers, or pounds vs. kilograms) and tracking these dimensions as calculations or comparisons are performed.

## Dyne

The dyne (symbol dyn, from Greek δύναμις, dynamis, meaning power, force) is a derived unit of force specified in the centimetre–gram–second (CGS) system of units, a predecessor of the modern SI.

## Electric charge

Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field.

## Electric current

An electric current is a flow of electric charge.

## Electric potential

An electric potential (also called the electric field potential, potential drop or the electrostatic potential) is the amount of work needed to move a unit positive charge from a reference point to a specific point inside the field without producing any acceleration.

## Electrical impedance

Electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied.

## Electrical reactance

In electrical and electronic systems, reactance is the opposition of a circuit element to a change in current or voltage, due to that element's inductance or capacitance.

## Electrical resistance and conductance

The electrical resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor.

In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space-time, carrying electromagnetic radiant energy.

## Electromotive force

Electromotive force, abbreviated emf (denoted \mathcal and measured in volts), is the electrical intensity or "pressure" developed by a source of electrical energy such as a battery or generator.

## Electron

The electron is a subatomic particle, symbol or, whose electric charge is negative one elementary charge.

## Electronvolt

In physics, the electronvolt (symbol eV, also written electron-volt and electron volt) is a unit of energy equal to approximately joules (symbol J).

## Electrostatic units

The electrostatic system of units (ESU) is a system of units used to measure quantities of electric charge, electric current, and voltage within the centimeter-gram-second (or "CGS") system of metric units.

## Elementary charge

The elementary charge, usually denoted as or sometimes, is the electric charge carried by a single proton, or equivalently, the magnitude of the electric charge carried by a single electron, which has charge.

## Encyclopedia.com

Encyclopedia.com is an online encyclopedia website.

## Energy

In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object.

## Ephemeris time

The term ephemeris time (often abbreviated ET) can in principle refer to time in connection with any astronomical ephemeris.

## Equivalent dose

Equivalent dose is a dose quantity H representing the stochastic health effects of low levels of ionizing radiation on the human body.

## Erg

The erg is a unit of energy and work equal to 10−7 joules.

## Etymology of electricity

The New Latin adjective electricus, originally meaning 'of amber', was first used to refer to amber's attractive properties by William Gilbert in his 1600 text De Magnete.

## Exponentiation

Exponentiation is a mathematical operation, written as, involving two numbers, the base and the exponent.

The farad (symbol: F) is the SI derived unit of electrical capacitance, the ability of a body to store an electrical charge.

## Foot (unit)

The foot (feet; abbreviation: ft; symbol: &prime;, the prime symbol) is a unit of length in the imperial and US customary systems of measurement.

## Force

In physics, a force is any interaction that, when unopposed, will change the motion of an object.

The French Academy of Sciences (French: Académie des sciences) is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research.

## French language

French (le français or la langue française) is a Romance language of the Indo-European family.

## Frequency

Frequency is the number of occurrences of a repeating event per unit of time.

## Full stop

The full point or full stop (British and broader Commonwealth English) or period (North American English) is a punctuation mark.

## Gabriel Mouton

Gabriel Mouton (1618 &ndash; 28 September 1694) was a French abbot and scientist.

## Gal (unit)

The gal (symbol: Gal), sometimes called galileo after Galileo Galilei, is a unit of acceleration used extensively in the science of gravimetry.

## Gauss (unit)

The gauss, abbreviated as G or Gs, is the cgs unit of measurement of magnetic flux density (or "magnetic induction") (B).

## General Conference on Weights and Measures

The General Conference on Weights and Measures (Conférence générale des poids et mesures – CGPM) is the supreme authority of the International Bureau of Weights and Measures (Bureau international des poids et mesures – BIPM), the inter-governmental organization established in 1875 under the terms of the Metre Convention (Convention du Mètre) through which Member States act together on matters related to measurement science and measurement standards.

## Geodesy

Geodesy, also known as geodetics, is the earth science of accurately measuring and understanding three of Earth's fundamental properties: its geometric shape, orientation in space, and gravitational field.

## Geophysics

Geophysics is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis.

## German language

German (Deutsch) is a West Germanic language that is mainly spoken in Central Europe.

## Giovanni Giorgi

Giovanni Giorgi (27 November 1871 – 19 August 1950) was an Italian physicist and electrical engineer who proposed the Giorgi system of measurement, the precursor to the International System of Units (SI).

## Gram

The gram (alternative spelling: gramme; SI unit symbol: g) (Latin gramma, from Greek γράμμα, grámma) is a metric system unit of mass.

## Grave (unit)

The grave was the original name of the kilogram, in an early version of the metric system between 1793 and 1795.

## Gray (unit)

The gray (symbol: Gy) is a derived unit of ionizing radiation dose in the International System of Units (SI).

## Ground state

The ground state of a quantum mechanical system is its lowest-energy state; the energy of the ground state is known as the zero-point energy of the system.

## Health care

Health care or healthcare is the maintenance or improvement of health via the prevention, diagnosis, and treatment of disease, illness, injury, and other physical and mental impairments in human beings.

## Heat

In thermodynamics, heat is energy transferred from one system to another as a result of thermal interactions.

## Hectare

The hectare (SI symbol: ha) is an SI accepted metric system unit of area equal to a square with 100 meter sides, or 10,000 m2, and is primarily used in the measurement of land.

## Henry (unit)

The henry (symbol: H) is the SI derived unit of electrical inductance.

## Hertz

The hertz (symbol: Hz) is the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second.

## History of the metre

In the aftermath of the French Revolution (1789), the traditional units of measure used in the Ancien Régime were replaced.

## Horsepower

Horsepower (hp) is a unit of measurement of power (the rate at which work is done).

## Hour

An hour (symbol: h; also abbreviated hr.) is a unit of time conventionally reckoned as of a day and scientifically reckoned as 3,599–3,601 seconds, depending on conditions.

## Hyperfine structure

In atomic physics, hyperfine structure refers to small shifts and splittings in the energy levels of atoms, molecules and ions, due to interaction between the state of the nucleus and the state of the electron clouds.

## Illuminance

In photometry, illuminance is the total luminous flux incident on a surface, per unit area.

## Inductance

In electromagnetism and electronics, inductance is the property of an electrical conductor by which a change in electric current through it induces an electromotive force (voltage) in the conductor.

## Institute for Reference Materials and Measurements

The Institute for Reference Materials and Measurements (IRMM), located in Geel, Belgium, is one of the seven institutes of the Joint Research Centre (JRC), a Directorate-General of the European Commission (EC).

## International Bureau of Weights and Measures

The International Bureau of Weights and Measures (Bureau international des poids et mesures) is an intergovernmental organization established by the Metre Convention, through which Member States act together on matters related to measurement science and measurement standards.

## International Committee for Weights and Measures

The International Committee for Weights and Measures (abbreviated CIPM from the French Comité international des poids et mesures) consists of eighteen persons, each of a different nationality, from Member States of the Metre Convention (Convention du Mètre) appointed by the General Conference on Weights and Measures (CGPM) whose principal task is to promote worldwide uniformity in units of measurement by taking direct action or by submitting proposals to the CGPM.

## International Electrotechnical Commission

The International Electrotechnical Commission (IEC; in French: Commission électrotechnique internationale) is an international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology".

## International Organization for Standardization

The International Organization for Standardization (ISO) is an international standard-setting body composed of representatives from various national standards organizations.

## International System of Quantities

The International System of Quantities (ISQ) is a system based on seven base quantities: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity.

## Introduction to the metric system

The metric system was developed during the French Revolution to replace the various measures previously used in France.

## Ion

An ion is an atom or molecule that has a non-zero net electrical charge (its total number of electrons is not equal to its total number of protons).

Ionizing radiation (ionising radiation) is radiation that carries enough energy to liberate electrons from atoms or molecules, thereby ionizing them.

## Iridium

Iridium is a chemical element with symbol Ir and atomic number 77.

## ISO 80000-1

ISO 80000-1:2009 is a standard describing scientific and mathematical quantities and their units.

## ISO/IEC 80000

ISO 80000 or IEC 80000 is an international standard promulgated jointly by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC).

## Isotopes of caesium

Caesium (55Cs; or cesium) has 40 known isotopes, making it, along with barium and mercury, the element with the most isotopes.

## Isotopes of krypton

There are 33 known isotopes of krypton (36Kr) with atomic mass numbers from 69 through 101.

## James Clerk Maxwell

James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish scientist in the field of mathematical physics.

## Jean-Pierre Christin

Jean-Pierre Christin (May 31, 1683 – January 19, 1755) was a French physicist, mathematician, astronomer and musician.

## John Wilkins

John Wilkins, (16141672) was an Anglican clergyman, natural philosopher and author, and was one of the founders of the Royal Society.

## Joint Committee for Guides in Metrology

The Joint Committee for Guides in Metrology (JCGM), is an organization in Sèvres that prepared the "Guide to the expression of uncertainty in measurement" (GUM) and the "International vocabulary of metrology – basic and general concepts and associated terms" (VIM).

## Joule

The joule (symbol: J) is a derived unit of energy in the International System of Units.

## Katal

The katal (symbol: kat) is the SI unit of catalytic activity.

## Kelvin

The Kelvin scale is an absolute thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics.

## Kibble balance

A Kibble balance (previously watt balance) is an electromechanical weight measuring instrument that measures the weight of a test object very precisely by the strength of an electric current and a voltage.

## Kilogram

The kilogram or kilogramme (symbol: kg) is the base unit of mass in the International System of Units (SI), and is defined as being equal to the mass of the International Prototype of the Kilogram (IPK, also known as "Le Grand K" or "Big K"), a cylinder of platinum-iridium alloy stored by the International Bureau of Weights and Measures at Saint-Cloud, France.

## Knot (unit)

The knot is a unit of speed equal to one nautical mile per hour, exactly 1.852 km/h (approximately 1.15078 mph).

## Latin America

Latin America is a group of countries and dependencies in the Western Hemisphere where Spanish, French and Portuguese are spoken; it is broader than the terms Ibero-America or Hispanic America.

## Length

In geometric measurements, length is the most extended dimension of an object.

## Letter case

Letter case (or just case) is the distinction between the letters that are in larger upper case (also uppercase, capital letters, capitals, caps, large letters, or more formally majuscule) and smaller lower case (also lowercase, small letters, or more formally minuscule) in the written representation of certain languages.

## Liberia

Liberia, officially the Republic of Liberia, is a country on the West African coast.

## List of international common standards

A list of common and basic information standards, that are related by their frequent and widespread use, and which are conventionally used internationally by industry and organizations.

## List of sovereign states and dependent territories in Europe

The list below includes all entities falling even partially under any of the various common definitions of Europe, geographical or political.

## Litre

The litre (SI spelling) or liter (American spelling) (symbols L or l, sometimes abbreviated ltr) is an SI accepted metric system unit of volume equal to 1 cubic decimetre (dm3), 1,000 cubic centimetres (cm3) or 1/1,000 cubic metre. A cubic decimetre (or litre) occupies a volume of 10 cm&times;10 cm&times;10 cm (see figure) and is thus equal to one-thousandth of a cubic metre. The original French metric system used the litre as a base unit. The word litre is derived from an older French unit, the litron, whose name came from Greek — where it was a unit of weight, not volume — via Latin, and which equalled approximately 0.831 litres. The litre was also used in several subsequent versions of the metric system and is accepted for use with the SI,, p. 124. ("Days" and "hours" are examples of other non-SI units that SI accepts.) although not an SI unit — the SI unit of volume is the cubic metre (m3). The spelling used by the International Bureau of Weights and Measures is "litre", a spelling which is shared by almost all English-speaking countries. The spelling "liter" is predominantly used in American English. One litre of liquid water has a mass of almost exactly one kilogram, because the kilogram was originally defined in 1795 as the mass of one cubic decimetre of water at the temperature of melting ice. Subsequent redefinitions of the metre and kilogram mean that this relationship is no longer exact.

## Long and short scales

The long and short scales are two of several large-number naming systems for integer powers of ten that use the same words with different meanings.

## Lumen (unit)

The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total quantity of visible light emitted by a source.

## Luminous flux

In photometry, luminous flux or luminous power is the measure of the perceived power of light.

## Luminous intensity

In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye.

## Lux

The lux (symbol: lx) is the SI derived unit of illuminance and luminous emittance, measuring luminous flux per unit area.

## Magnetic field

A magnetic field is a vector field that describes the magnetic influence of electrical currents and magnetized materials.

## Magnetic flux

In physics, specifically electromagnetism, the magnetic flux (often denoted or) through a surface is the surface integral of the normal component of the magnetic field B passing through that surface.

## Mass

Mass is both a property of a physical body and a measure of its resistance to acceleration (a change in its state of motion) when a net force is applied.

## Mathematician

A mathematician is someone who uses an extensive knowledge of mathematics in his or her work, typically to solve mathematical problems.

## Maxwell (unit)

The maxwell (symbol: Mx) is the CGS (centimetre-gram-second) unit of magnetic flux.

## Melting point

The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid at atmospheric pressure.

## Meridian (geography)

A (geographical) meridian (or line of longitude) is the half of an imaginary great circle on the Earth's surface, terminated by the North Pole and the South Pole, connecting points of equal longitude.

## Metre

The metre (British spelling and BIPM spelling) or meter (American spelling) (from the French unit mètre, from the Greek noun μέτρον, "measure") is the base unit of length in some metric systems, including the International System of Units (SI).

## Metre Convention

The Metre Convention (Convention du Mètre), also known as the Treaty of the Metre, is an international treaty that was signed in Paris on 20 May 1875 by representatives of 17 nations (Argentina, Austria-Hungary, Belgium, Brazil, Denmark, France, Germany, Italy, Peru, Portugal, Russia, Spain, Sweden and Norway, Switzerland, Turkey, United States of America, and Venezuela).

## Metre per second squared

The metre per second squared is the unit of acceleration in the International System of Units (SI).

## Metre–tonne–second system of units

The metre–tonne–second or MTS system of units is a system of physical units.

## Metric prefix

A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or fraction of the unit.

## Metric system

The metric system is an internationally adopted decimal system of measurement.

## Metrication

Metrication or metrification is conversion to the metric system of units of measurement.

## Metrology

Metrology is the science of measurement.

## Millimeter of mercury

A millimeter of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high and now defined as precisely pascals.

## Minute

The minute is a unit of time or angle.

## Minute and second of arc

A minute of arc, arcminute (arcmin), arc minute, or minute arc is a unit of angular measurement equal to of one degree.

## MKS system of units

The MKS system of units is a physical system of units that expresses any given measurement using base units of the metre, kilogram, and/or second (MKS).

## Mole (unit)

The mole, symbol mol, is the SI unit of amount of substance.

## Molecular mass

Relative Molecular mass or molecular weight is the mass of a molecule.

## Molecule

A molecule is an electrically neutral group of two or more atoms held together by chemical bonds.

## Multiplication

Multiplication (often denoted by the cross symbol "×", by a point "⋅", by juxtaposition, or, on computers, by an asterisk "∗") is one of the four elementary mathematical operations of arithmetic; with the others being addition, subtraction and division.

## Myanmar

Myanmar, officially the Republic of the Union of Myanmar and also known as Burma, is a sovereign state in Southeast Asia.

## National Institute of Standards and Technology

The National Institute of Standards and Technology (NIST) is one of the oldest physical science laboratories in the United States.

## Nautical mile

A nautical mile is a unit of measurement defined as exactly.

Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.

## Neper

The neper (symbol: Np) is a logarithmic unit for ratios of measurements of physical field and power quantities, such as gain and loss of electronic signals.

## Newton (unit)

The newton (symbol: N) is the International System of Units (SI) derived unit of force.

## Newton's laws of motion

Newton's laws of motion are three physical laws that, together, laid the foundation for classical mechanics.

## Non-SI units mentioned in the SI

This is a list of units that are not defined as part of the International System of Units (SI), but are otherwise mentioned in the SI, because either the General Conference on Weights and Measures (CGPM) accepts their use as being multiples or submultiples of SI-units, they have important contemporary application worldwide, or are otherwise commonly encountered worldwide.

## Oersted

The oersted (symbol Oe) is the unit of the auxiliary magnetic field '''H''' in the centimetre–gram–second system of units (CGS).

## Ohm

The ohm (symbol: Ω) is the SI derived unit of electrical resistance, named after German physicist Georg Simon Ohm.

## Outline of the metric system

The following outline is provided as an overview of and topical guide to the metric system: Metric system &ndash; various loosely related systems of measurement that trace their origin to the decimal system of measurement introduced in France during the French Revolution.

## Oxford University Press

Oxford University Press (OUP) is the largest university press in the world, and the second oldest after Cambridge University Press.

## Pascal (unit)

The pascal (symbol: Pa) is the SI derived unit of pressure used to quantify internal pressure, stress, Young's modulus and ultimate tensile strength.

## Permeability (earth sciences)

Permeability in fluid mechanics and the earth sciences (commonly symbolized as κ, or k) is a measure of the ability of a porous material (often, a rock or an unconsolidated material) to allow fluids to pass through it.

## Phot

A phot (ph) is a photometric unit of illuminance, or luminous flux through an area.

## Physical quantity

A physical quantity is a physical property of a phenomenon, body, or substance, that can be quantified by measurement.or we can say that quantities which we come across during our scientific studies are called as the physical quantities...

## Physikalisch-Technische Bundesanstalt

The Physikalisch-Technische Bundesanstalt (PTB) is the national metrology institute of the Federal Republic of Germany, with scientific and technical service tasks.

## Planck constant

The Planck constant (denoted, also called Planck's constant) is a physical constant that is the quantum of action, central in quantum mechanics.

## Platinum

Platinum is a chemical element with symbol Pt and atomic number 78.

## Platinum-iridium alloy

Platinum-iridium alloys are alloys of the platinum group precious metals platinum and iridium.

## Poise (unit)

The poise (symbol P) is the unit of dynamic viscosity (absolute viscosity) in the centimetre–gram–second system of units.

## Pound (mass)

The pound or pound-mass is a unit of mass used in the imperial, United States customary and other systems of measurement.

## Power (physics)

In physics, power is the rate of doing work, the amount of energy transferred per unit time.

## Pressure

Pressure (symbol: p or P) is the force applied perpendicular to the surface of an object per unit area over which that force is distributed.

## Printing press

A printing press is a device for applying pressure to an inked surface resting upon a print medium (such as paper or cloth), thereby transferring the ink.

## Proper noun

A proper noun is a noun that in its primary application refers to a unique entity, such as London, Jupiter, Sarah, or Microsoft, as distinguished from a common noun, which usually refers to a class of entities (city, planet, person, corporation), or non-unique instances of a specific class (a city, another planet, these persons, our corporation).

## Properties of water

Water is a polar inorganic compound that is at room temperature a tasteless and odorless liquid, which is nearly colorless apart from an inherent hint of blue. It is by far the most studied chemical compound and is described as the "universal solvent" and the "solvent of life". It is the most abundant substance on Earth and the only common substance to exist as a solid, liquid, and gas on Earth's surface. It is also the third most abundant molecule in the universe. Water molecules form hydrogen bonds with each other and are strongly polar. This polarity allows it to separate ions in salts and strongly bond to other polar substances such as alcohols and acids, thus dissolving them. Its hydrogen bonding causes its many unique properties, such as having a solid form less dense than its liquid form, a relatively high boiling point of 100 °C for its molar mass, and a high heat capacity. Water is amphoteric, meaning that it is both an acid and a base—it produces + and - ions by self-ionization.

## Proposed redefinition of SI base units

The International Committee for Weights and Measures (CIPM) has proposed revised definitions of the SI base units, for consideration at the 26th General Conference on Weights and Measures (CGPM).

The radian (SI symbol rad) is the SI unit for measuring angles, and is the standard unit of angular measure used in many areas of mathematics.

In radiometry, radiant flux or radiant power is the radiant energy emitted, reflected, transmitted or received, per unit time, and spectral flux or spectral power is the radiant flux per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength.

Radioactive decay (also known as nuclear decay or radioactivity) is the process by which an unstable atomic nucleus loses energy (in terms of mass in its rest frame) by emitting radiation, such as an alpha particle, beta particle with neutrino or only a neutrino in the case of electron capture, gamma ray, or electron in the case of internal conversion.

## Rapeseed

Rapeseed (Brassica napus), also known as rape, oilseed rape, (and, in the case of one particular group of cultivars, canola), is a bright-yellow flowering member of the family Brassicaceae (mustard or cabbage family), cultivated mainly for its oil-rich seed.

## Relative change and difference

In any quantitative science, the terms relative change and relative difference are used to compare two quantities while taking into account the "sizes" of the things being compared.

## Sèvres

Sèvres is a commune in the southwestern suburbs of Paris, France.

## Second

The second is the SI base unit of time, commonly understood and historically defined as 1/86,400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each.

## SI base unit

The International System of Units (SI) defines seven units of measure as a basic set from which all other SI units can be derived.

## SI derived unit

SI derived units are units of measurement derived from the seven base units specified by the International System of Units (SI).

## Siemens (unit)

The siemens (symbol: S) is the derived unit of electric conductance, electric susceptance and electric admittance in the International System of Units (SI).

## Sievert

The sievert (symbol: SvNot be confused with the sverdrup or the svedberg, two non-SI units that sometimes use the same symbol.) is a derived unit of ionizing radiation dose in the International System of Units (SI) and is a measure of the health effect of low levels of ionizing radiation on the human body.

## Slash (punctuation)

The slash is an oblique slanting line punctuation mark.

## Solid angle

In geometry, a solid angle (symbol) is a measure of the amount of the field of view from some particular point that a given object covers.

## Speed of light

The speed of light in vacuum, commonly denoted, is a universal physical constant important in many areas of physics.

## Spermaceti

Spermaceti (from Greek sperma meaning "seed", and ceti, the genitive form of "whale") is a waxy substance found in the head cavities of the sperm whale (and, in smaller quantities, in the oils of other whales).

## Standard (metrology)

In metrology (the science of measurement), a standard (or etalon) is an object, system, or experiment that bears a defined relationship to a unit of measurement of a physical quantity.

## Standard gravity

The standard acceleration due to gravity (or standard acceleration of free fall), sometimes abbreviated as standard gravity, usually denoted by or, is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth.

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## Stilb (unit)

The stilb (sb) is the CGS unit of luminance for objects that are not self-luminous.

## Stress (mechanics)

In continuum mechanics, stress is a physical quantity that expresses the internal forces that neighboring particles of a continuous material exert on each other, while strain is the measure of the deformation of the material.

## Symbol

A symbol is a mark, sign or word that indicates, signifies, or is understood as representing an idea, object, or relationship.

## System of measurement

A system of measurement is a collection of units of measurement and rules relating them to each other.

## Technical standard

A technical standard is an established norm or requirement in regard to technical systems.

## Temperature

Temperature is a physical quantity expressing hot and cold.

## Temperature measurement

Temperature measurement, also known as thermometry, describes the process of measuring a current local temperature for immediate or later evaluation.

## Tesla (unit)

The tesla (symbol T) is a derived unit of magnetic flux density (informally, magnetic field strength) in the International System of Units.

## Thermodynamic temperature

Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics.

## Time

Time is the indefinite continued progress of existence and events that occur in apparently irreversible succession from the past through the present to the future.

## Tonne

The tonne (Non-SI unit, symbol: t), commonly referred to as the metric ton in the United States, is a non-SI metric unit of mass equal to 1,000 kilograms;.

## Torque

Torque, moment, or moment of force is rotational force.

## Triple point

In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.

## Tropical year

A tropical year (also known as a solar year) is the time that the Sun takes to return to the same position in the cycle of seasons, as seen from Earth; for example, the time from vernal equinox to vernal equinox, or from summer solstice to summer solstice.

## Typewriter

A typewriter is a mechanical or electromechanical machine for writing characters similar to those produced by printer's movable type.

## Unified atomic mass unit

The unified atomic mass unit or dalton (symbol: u, or Da) is a standard unit of mass that quantifies mass on an atomic or molecular scale (atomic mass).

## Unified Code for Units of Measure

The Unified Code for Units of Measure (the UCUM) is a system of codes for unambiguously representing measurement units to both humans and machines.

## Unit of measurement

A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity.

## United States

The United States of America (USA), commonly known as the United States (U.S.) or America, is a federal republic composed of 50 states, a federal district, five major self-governing territories, and various possessions.

## University of Edinburgh

The University of Edinburgh (abbreviated as Edin. in post-nominals), founded in 1582, is the sixth oldest university in the English-speaking world and one of Scotland's ancient universities.

## University of North Carolina

The University of North Carolina is a multi-campus public university system composed of all 16 of North Carolina's public universities, as well as the NC School of Science and Mathematics, the nation's first public residential high school for gifted students.

## Vacuum

Vacuum is space devoid of matter.

## Velocity

The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time.

## Viscosity

The viscosity of a fluid is the measure of its resistance to gradual deformation by shear stress or tensile stress.

## Volt

The volt (symbol: V) is the derived unit for electric potential, electric potential difference (voltage), and electromotive force.

## Voltage

Voltage, electric potential difference, electric pressure or electric tension (formally denoted or, but more often simply as V or U, for instance in the context of Ohm's or Kirchhoff's circuit laws) is the difference in electric potential between two points.

## Washington, D.C.

Washington, D.C., formally the District of Columbia and commonly referred to as Washington or D.C., is the capital of the United States of America.

## Watt

The watt (symbol: W) is a unit of power.

## Wavelength

In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.

## Weber (unit)

In physics, the weber (symbol: Wb) is the SI unit of magnetic flux.

## Weight

In science and engineering, the weight of an object is related to the amount of force acting on the object, either due to gravity or to a reaction force that holds it in place.

## Wilhelm Eduard Weber

Wilhelm Eduard Weber (24 October 1804 – 23 June 1891) was a German physicist and, together with Carl Friedrich Gauss, inventor of the first electromagnetic telegraph.

## William Thomson, 1st Baron Kelvin

William Thomson, 1st Baron Kelvin, (26 June 1824 – 17 December 1907) was a Scots-Irish mathematical physicist and engineer who was born in Belfast in 1824.

## Word processor

A word processor is a computer program or device that provides for input, editing, formatting and output of text, often plus other features.

## Work (physics)

In physics, a force is said to do work if, when acting, there is a displacement of the point of application in the direction of the force.

## World War II

World War II (often abbreviated to WWII or WW2), also known as the Second World War, was a global war that lasted from 1939 to 1945, although conflicts reflecting the ideological clash between what would become the Allied and Axis blocs began earlier.

## Yale University Press

Yale University Press is a university press associated with Yale University.

## References

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