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For example, two states of a property may be compared by ratio, difference, or ordinal preference. The type is commonly not explicitly expressed, but implicit in the definition of a measurement procedure. The magnitude is the numerical value of the characterization, usually obtained with a suitably chosen measuring instrument.
The following is a topical outline of the English language Wikipedia articles on the topic of metrology and measurement. Metrology is the science of measurement and its application. Metrology is the science of measurement and its application.
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. [1] Standards are the fundamental reference for a system of weights and measures, against which all other measuring devices are compared.
Metrology is a wide reaching field, but can be summarized through three basic activities: the definition of internationally accepted units of measurement, the realisation of these units of measurement in practice, and the application of chains of traceability (linking measurements to reference standards).
For example, a length that is significantly longer or shorter than 1 metre can be represented in units that are a power of 10 or 1000 metres. This differs from many older systems in which the ratio of different units varied. For example, 12 inches is one foot, but the larger unit in the same system, the mile is not a power of 12 feet. It is ...
In antiquity, systems of measurement were defined locally: the different units might be defined independently according to the length of a king's thumb or the size of his foot, the length of stride, the length of arm, or maybe the weight of water in a keg of specific size, perhaps itself defined in hands and knuckles.
Pyrometers principle: temperature dependence of spectral intensity of light (Planck's law), i.e. the color of the light relates to the temperature of its source, range: from about −50 °C to +4000 °C, note: measurement of thermal radiation (instead of thermal conduction, or thermal convection) means: no physical contact becomes necessary in ...
Note that neither the names nor the symbols used for the physical quantities are international standards. Some quantities are known as several different names such as the magnetic B-field which is known as the magnetic flux density , the magnetic induction or simply as the magnetic field depending on the context.