The centimetre–gram–second system of units is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, the second as the unit of time. All CGS mechanical units are unambiguously derived from these three base units, but there are several different ways of extending the CGS system to cover electromagnetism; the CGS system has been supplanted by the MKS system based on the metre and second, in turn extended and replaced by the International System of Units. In many fields of science and engineering, SI is the only system of units in use but there remain certain subfields where CGS is prevalent. In measurements of purely mechanical systems, the differences between CGS and SI are straightforward and rather trivial. For example, the CGS unit of force is the dyne, defined as 1 g⋅cm/s2, so the SI unit of force, the newton, is equal to 100,000 dynes. On the other hand, in measurements of electromagnetic phenomena, converting between CGS and SI is more subtle.

Formulas for physical laws of electromagnetism need to be adjusted depending on which system of units one uses. This is because there is no one-to-one correspondence between electromagnetic units in SI and those in CGS, as is the case for mechanical units. Furthermore, within CGS, there are several plausible choices of electromagnetic units, leading to different unit "sub-systems", including Gaussian units, "ESU", "EMU", Lorentz–Heaviside units. Among these choices, Gaussian units are the most common today, "CGS units" used refers to CGS-Gaussian units; the CGS system goes back to a proposal in 1832 by the German mathematician Carl Friedrich Gauss to base a system of absolute units on the three fundamental units of length and time. Gauss chose the units of millimetre and second. In 1873, a committee of the British Association for the Advancement of Science, including physicists James Clerk Maxwell and William Thomson recommended the general adoption of centimetre and second as fundamental units, to express all derived electromagnetic units in these fundamental units, using the prefix "C.

G. S. unit of...". The sizes of many CGS units turned out to be inconvenient for practical purposes. For example, many everyday objects are hundreds or thousands of centimetres long, such as humans and buildings, thus the CGS system never gained wide general use outside the field of science. Starting in the 1880s, more by the mid-20th century, CGS was superseded internationally for scientific purposes by the MKS system, which in turn developed into the modern SI standard. Since the international adoption of the MKS standard in the 1940s and the SI standard in the 1960s, the technical use of CGS units has declined worldwide, in the United States more than elsewhere. CGS units are today no longer accepted by the house styles of most scientific journals, textbook publishers, or standards bodies, although they are used in astronomical journals such as The Astrophysical Journal. CGS units are still encountered in technical literature in the United States in the fields of material science and astronomy.

The continued usage of CGS units is most prevalent in magnetism and related fields because the B and H fields have the same units in free space and there is a lot of potential for confusion when converting published measurements from cgs to MKS. The units gram and centimetre remain useful as prefixed units within the SI system for instructional physics and chemistry experiments, where they match the small scale of table-top setups. However, where derived units are needed, the SI ones are used and taught instead of the CGS ones today. For example, a physics lab course might ask students to record lengths in centimetres, masses in grams, but force in newtons, a usage consistent with the SI system. In mechanics, the CGS and SI systems of units are built in an identical way; the two systems differ only in the scale of two out of the three base units, while the third unit is the same in both systems. There is a one-to-one correspondence between the base units of mechanics in CGS and SI, the laws of mechanics are not affected by the choice of units.

The definitions of all derived units in terms of the three base units are therefore the same in both systems, there is an unambiguous one-to-one correspondence of derived units: v = d x d t F = m d 2 x d t 2 E = ∫ F → ⋅ d x → p = F L 2 η = τ / d v d x (dynamic viscosity defined as shear stress per unit

Maria Korchinska was a distinguished 20th-century Russian harpist and one of the leading 20th-century harpists in Great Britain. Korchinska entered the Moscow Conservatory to study both piano and harp in 1903 but on the advice of her father decided to concentrate on the harp from 1907, her father believed that Russia was entering a time of great change and that given the high number of pianists in Russia it would be easier for his daughter to find work as a harpist than as a pianist. In 1911 she won the first Gold Medal given to a harpist by the Moscow Conservatory. In 1919 she became the Professor of Harp at the Conservatory as well as the Principal Harpist at the Bolshoi Orchestra. Korchinska was a founding member of the Persimfans, the famous "Orchestra without a conductor", she was one of the many musicians. In 1922 Korchinska married Count Constantine Benckendorff, her daughter Nathalie was born in Moscow in September 1923, in 1946, she married the British art historian Humphrey Brooke. The Russian Civil War had seen the confiscation of her husband's estate and conditions were difficult.

Korchinska had to carry her father's body to his funeral. In 1924 the family decided to leave Russia for Great Britain, taking with them two Lyon & Healy harps. One of these had been purchased in exchange for a bag of salt. In Great Britain, Korchinska founded the UK Harp Association and had a successful career as a soloist and ensemble player, she was the first harpist to play at the Glyndebourne Festival Opera, was a founding member of the Wigmore Ensemble and was the first British judge at the Israeli Harp competition. Her son Alexander was born in England in July 1926. Bax's Fantasy Sonata for Harp was dedicated to her and she gave the first performance in 1927, her portrait was taken by Norman Parkinson in 1953 and is now part of the National Portrait Gallery's collection. She performed in the premieres of several Benjamin Britten works including the Festival of Carols. During World War II she traveled ceaselessly throughout the country to play. In her 1969 BBC interview "Studio Portrait" she said: "I played....

Underground in caves near Lewes, where a piano could not survive the damp. I played in cathedrals and clubs and YMCAs and several times in secret camps and aerodromes, without having the faintest idea of where I was. My life was spent in the black-out trying to find my way. I was lucky. Several times I was given up, but arrived with my instrument at the last moment hot and scared because of the bombing, but able to play." Korchinska founded Harp Week in the Netherlands alongside Phia Berghout. She practised three hours every day until her death in 1979. Favourite pieces included the A Ceremony of Carols by Danse Sacrée by Debussy, she taught Karen Vaughan Head of Harp at the Royal Academy of Music in London. Nineteenth- And Twentieth-Century Harpists: A Bio-Critical Sourcebook - Wenonah Milton Govea - Google Books pp. 145–150. Raymond Leppard on Music: Anthology of Critical and Autobiographical Writings - Raymond Leppard - Google Books p. 85. Gramophone - Google Books All Music Guide to Classical Music: The Definitive Guide to Classical Music - Google Books Music and Musicians - Google Books npg.org.uk allmusic.com Images of Maria Korchinska at National Portrait Gallery, London

Understanding is a psychological process related to an abstract or physical object, such as a person, situation, or message whereby one is able to think about it and use concepts to deal adequately with that object. Understanding is an object of understanding. Understanding implies abilities and dispositions with respect to an object of knowledge that are sufficient to support intelligent behaviour. Understanding is though not always, related to learning concepts, sometimes the theory or theories associated with those concepts. However, a person may have a good ability to predict the behaviour of an object, animal or system—and therefore may, in some sense, understand it—without being familiar with the concepts or theories associated with that object, animal or system in their culture, they may have developed their own distinct concepts and theories, which may be equivalent, better or worse than the recognised standard concepts and theories of their culture. Thus, understanding is correlated with the ability to make inferences.

One understands the weather if one is able to predict and/or give an explanation of some of its features, etc. A psychiatrist understands another person's anxieties if he/she knows that person's anxieties, their causes, can give useful advice on how to cope with the anxiety. One understands a piece of reasoning or an argument if one can consciously reproduce the information content conveyed by the message. One understands a language to the extent that one can reproduce the information content conveyed by a broad range of spoken utterances or written messages in that language. Someone who has a more sophisticated understanding, more predictively accurate understanding, and/or an understanding that allows them to make explanations that others judge to be better, of something, is said to understand that thing "deeply". Conversely, someone who has a more limited understanding of a thing is said to have a "shallow" understanding. However, the depth of understanding required to usefully participate in an occupation or activity may vary greatly.

For example, consider multiplication of integers. Starting from the most shallow level of understanding, we have the following possibilities: A small child may not understand what multiplication is, but may understand that it is a type of mathematics that they will learn when they are older at school; this is "understanding of context". Understanding that a concept is not part of one's current knowledge is, in itself, a type of understanding. A older child may understand that multiplication of two integers can be done, at least when the numbers are between 1 and 12, by looking up the two numbers in a times table, they may be able to memorise and recall the relevant times table in order to answer a multiplication question such as "2 times 4 is what?". This is a simple form of operational understanding. A yet older child may understand that multiplication of larger numbers can be done using a different method, such as long multiplication, or using a calculator; this is a more advanced form of operational understanding because it supports answering a wider range of questions of the same type.

A teenager may understand that multiplication is repeated addition, but not understand the broader implications of this. For example, when their teacher refers to multiplying 6 by 3 as "adding 6 to itself 3 times", they may understand that the teacher is talking about two equivalent things. However, they might not understand how to apply this knowledge to implement multiplication as an algorithm on a computer using only addition and looping as basic constructs; this level of understanding is "understanding a definition". A teenager may understand the mathematical idea of abstracting over individual whole numbers as variables, how to efficiently solve algebraic equations involving multiplication by such variables, such as 2 x = 6; this is "relational understanding". An undergraduate studying mathematics may come to learn that "the integers equipped with multiplication" is one example of a range of mathematical structures called monoids, that theorems about monoids apply well to multiplication and other types of monoids.

For the purpose of operating a cash register at McDonald's, a person does not need a deep understanding of the multiplication involved in calculating the total price of two Big Macs. However, for the purpose of contributing to number theory research, a person would need to have a deep understanding of multiplication — along with other relevant arithmetical concepts such as division and prime numbers, it is possible for a person, or a piece of "intelligent" software, that in reality only has a shallow understanding of a topic, to appear to have a deeper understanding than they do, when the right questions are asked of it. The most obvious way this can happen is by memorization of correct answers to known questions, but there are other, more subtle ways that a person or computer can deceive somebody about their level of understanding, too; this is a risk with artificial intelligence, in which the ability of a piece of artificial intelligence software to quickly try out