query: subclass_of si derived unit
supports: 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 a measurement is 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. A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different concepts and experiences. All communication (and data processing) is achieved through the use of symbols.Symbols take the form of words, sounds, gestures, ideas or visual images and are used to convey other ideas and beliefs. For example, a red octagon may be a symbol for "STOP". On a map, a blue line might represent a river. Numerals are symbols for numbers. Alphabetic letters may be symbols for sounds. Personal names are symbols representing individuals. A red rose may symbolize love and compassion. The variable 'x', in a mathematical equation, may symbolize the position of a particle in space. 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 quantity. Any other value of that quantity can be expressed as a simple multiple of the unit of measurement. A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce. Systems of measurement in modern use include the metric system, the imperial system, and United States customary units. The International System of Units (; abbreviated as SI) is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units. The system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. Quantity is a property that can exist as a magnitude or multitude. Quantities can be compared in terms of "more", "less", or "equal", or by assigning a numerical value in terms of a unit of measurement. Quantity is among the basic classes of things along with quality, substance, change, and relation. Some quantities are such by their inner nature (as number), while others are functioning as states (properties, dimensions, attributes) of things such as heavy and light, long and short, broad and narrow, small and great, or much and little. A small quantity is sometimes referred to as a quantulum. The metric system is an internationally agreed decimal system of measurement. It was originally based on the and the introduced by the French First Republic in 1799, but over the years the definitions of the metre and the kilogram have been refined, and the metric system has been extended to incorporate many more units. Although a number of variants of the metric system emerged in the late nineteenth and early twentieth centuries, the term is now often used as a synonym for "SI" or the "International System of Units"the official system of measurement in almost every country in the world. The International System of Units ( SI ) specifies a set of seven base units from which all other SI units of measurement are derived . Each of these other units ( SI derived units ) is either dimensionless or can be expressed as a product of ( positive or negative , but usually integral ) powers of one or more of the base units . For example , the SI derived unit of area is the square metre ( m2 ) , and the SI derived unit of density is the kilogram per cubic metre ( kg / m3 or kg m  3 ) . The degree Celsius ( see the table below ) has a somewhat unclear status , and is arguably an exception to this rule . The names of SI units are written in lowercase . The symbols for units named after persons , however , are always written with an uppercase initial letter ( e.g. the symbol for the hertz is `` Hz '' ; but the symbol for the metre is `` m '' ) .
candidates: application base collection commerce convention country event idea interval map mark measurement metre metric metrology number object octagon official particle people property quantity ratio relationship republic river set symbol synonym system system of measurement term unit of measurement value variable word
answer: unit of measurement