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Google is also the largest search engine, mapping and navigation application, email provider, office suite, online video platform, photo and cloud storage provider, mobile operating system, web browser, machine learning framework, and AI virtual assistant provider in the world as measured by market share. [18]
The number π (/paɪ/; spelled out as "pi") is a mathematical constant that is the ratio of a circle's circumference to its diameter, approximately equal to 3.14159. The number π appears in many formulae across mathematics and physics. It is an irrational number, meaning that it cannot be expressed exactly as a ratio of two integers, although ...
ISO 3166-1 ( Codes for the representation of names of countries and their subdivisions – Part 1: Country codes) is a standard defining codes for the names of countries, dependent territories, and special areas of geographical interest. It is the first part of the ISO 3166 standard published by the International Organization for Standardization .
- Definition
- Lexicographic Conventions
- Realisation of Units
- Organizational Status
- History
- Related Units
The International System of Units consists of a set of defining constants with corresponding base units, derived units, and a set of decimal-based multipliers that are used as prefixes.: 125
Unit names
According to the SI Brochure,: 148 unit names should be treated as common nouns of the context language. This means that they should be typeset in the same character set as other common nouns (e.g. Latin alphabet in English, Cyrillic script in Russian, etc.), following the usual grammatical and orthographical rules of the context language. For example, in English and French, even when the unit is named after a person and its symbol begins with a capital letter, the unit name in running text s...
Unit symbols and the values of quantities
Symbols of SI units are intended to be unique and universal, independent of the context language.: 130–35 The SI Brochure has specific rules for writing them.: 130–35 In addition, the SI Brochure provides style conventions for among other aspects of displaying quantities units: the quantity symbols, formatting of numbers and the decimal marker, expressing measurement uncertainty, multiplication and division of quantity symbols, and the use of pure numbers and various angles.: 147 In the Unite...
Metrologists carefully distinguish between the definition of a unit and its realisation. The SI units are defined by declaring that seven defining constants: 125–129 have certain exact numerical values when expressed in terms of their SI units. The realisation of the definition of a unit is the procedure by which the definition may be used to estab...
The International System of Units, or SI,: 123 is a decimal and metric system of units established in 1960 and periodically updated since then. The SI has an official status in most countries, including the United States, Canada, and the United Kingdom, although these three countries are among the handful of nations that, to various degrees, also c...
CGS and MKS systems
The concept of a system of units emerged a hundred years before the SI.In the 1860s, James Clerk Maxwell, William Thomson (later Lord Kelvin), and others working under the auspices of the British Association for the Advancement of Science, building on previous work of Carl Gauss, developed the centimetre–gram–second system of units or cgs system in 1874. The systems formalised the concept of a collection of related units called a coherent system of units. In a coherent system, base units comb...
Metre Convention
A French-inspired initiative for international cooperation in metrology led to the signing in 1875 of the Metre Convention, also called Treaty of the Metre, by 17 nations.[e]: 353–354 The General Conference on Weights and Measures (French: Conférence générale des poids et mesures – CGPM), which was established by the Metre Convention, brought together many international organisations to establish the definitions and standards of a new system and to standardise the rules for writing and presen...
Giovanni Giorgi and the problem of electrical units
At the close of the 19th century three different systems of units of measure existed for electrical measurements: a CGS-based system for electrostatic units, also known as the Gaussian or ESU system, a CGS-based system for electromechanical units (EMU), and an International system based on units defined by the Metre Convention for electrical distribution systems.Attempts to resolve the electrical units in terms of length, mass, and time using dimensional analysis was beset with difficulties –...
Non-SI units accepted for use with SI
Many non-SI units continue to be used in the scientific, technical, and commercial literature. Some units are deeply embedded in history and culture, and their use has not been entirely replaced by their SI alternatives. The CIPM recognised and acknowledged such traditions by compiling a list of non-SI units accepted for use with SI,including the hour, minute, degree of angle, litre, and decibel.
Metric units not recognised by SI
Although the term metric system is often used as an informal alternative name for the International System of Units, other metric systems exist, some of which were in widespread use in the past or are even still used in particular areas. There are also individual metric units such as the sverdrup and the darcythat exist outside of any system of units. Most of the units of the other metric systems are not recognised by the SI.
Unacceptable uses
Sometimes, SI unit name variations are introduced, mixing information about the corresponding physical quantity or the conditions of its measurement; however, this practice is unacceptable with the SI. "Unacceptability of mixing information with units: When one gives the value of a quantity, any information concerning the quantity or its conditions of measurement must be presented in such a way as not to be associated with the unit."Instances include: "watt-peak" and "watt RMS"; "geopotential...
Dymaxion map of the world with the 30 largest countries and territories by area This is a list of the world's countries and their dependencies by land, water, and total area, ranked by total area.The entries in this list include, but are not limited to, those in the ISO 3166-1 standard, which includes sovereign states and dependent territories.
Ethnologue (2023) The following languages are listed as having 45 million or more total speakers in the 26th edition of Ethnologue published in 2023. This section does not include entries that Ethnologue identifies as macrolanguages encompassing all their respective varieties, such as Arabic, Lahnda, Persian, Malay, Pashto, and Chinese.
