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Encyclopedia > Measurement

Measurement is the estimation of the magnitude of some attribute of an object, such as its length or weight, relative to a unit of measurement. Measurement usually involves using a measuring instrument, such as a ruler or scale, which is calibrated to compare the object to some standard, such as a meter or a kilogram. In science, however, where accurate measurement is crucial, a measurement is understood to have three parts: first, the measurement itself, second, the margin of error, and third, the confidence level -- that is, the probability that the actual property of the physical object is within the margin of error. For example, we might measure the length of an object as 2.34 meters plus or minus 0.01 meter, with a 95% confidence level.


Metrology is the scientific study of measurement. In measurement theory a measurement is an observation that reduces an uncertainty expressed as a quantity. As a verb, measurement is making such observations[1]. It includes the estimation of a physical quantity such as distance, energy, temperature, or time. It could also include such things as assessment of attitudes, values and perception in surveys or the testing of aptitudes of individuals. Metrology (from Greek metron (measure), and -logy) is the science of measurement. ...


In the physical sciences, measurement is most commonly thought of as the ratio of some physical quantity to a standard quantity of the same type, thus a measurement of length is the ratio of a physical length to some standard length, such as a standard meter. Measurements are usually given in terms of a real number times a unit of measurement, for example 2.53 meters, but sometimes measurements use complex numbers, as in measurements of electrical impedance. Electrical impedance, or simply impedance, is a measure of opposition to a sinusoidal alternating electric current. ...

Contents

Observations and error

The act of measuring often requires an instrument designed and calibrated for that purpose, such as a thermometer, speedometer, weighing scale, or voltmeter. Surveys and tests are also referred to as "measurement instruments" in academic testing, aptitude testing, voter polls, etc. A common mercury thermometer A thermometer is a device that measures temperature or temperature gradient, using a variety of different principles. ... Speedometer gauge on a car, showing the speed of the vehicle in miles and kilometres per hour on the out– and inside respectively. ... Digital kitchen scales. ... Two digital voltmeters. ...


Measurements almost always have an error and therefore uncertainty. In fact, the reduction—not necessarily the elimination—of uncertainty is central to the concept of measurement. Measurement errors are often assumed to be normally distributed about the true value of the measured quantity. Under this assumption, every measurement has three components: the estimate, the error bound, and the probability that the actual magnitude lies within the error bound of the estimate. For example, a measurement of the length of a plank might result in a measurement of 2.53 meters plus or minus 0.01 meter, with a probability of 99%. Measurement is the determination of the size or magnitude of something. ... The normal distribution, also called the Gaussian distribution, is an important family of continuous probability distributions, applicable in many fields. ...


The initial state of uncertainty, prior to any observations, is necessary to assess when using statistical methods that rely on prior knowledge (Bayesian methods,Applied Information Economics). This can be done with calibrated probability assessment. Bayesian inference is statistical inference in which evidence or observations are used to update or to newly infer the probability that a hypothesis may be true. ... The creator of or main contributor to this page may have a conflict of interest with the subject of this article. ... Calibrated Probability Assessments are subjective probabilities assigned by individuals who have been trained to assess probabilities in a way that historically represents their uncertainty[1][2]. In other words, when a calibrated person says they are 80% confident in each of 100 predictions they made, they will get about 80...


Measurement is fundamental in science; it is one of the things that distinguishes science from pseudoscience. It is easy to come up with a theory about nature, hard to come up with a scientific theory that predicts measurements with great accuracy. Measurement is also essential in industry, commerce, engineering, construction, manufacturing, pharmaceutical production, and electronics.

When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of science. —LORD KELVIN

History of measurement

The word measurement comes from the Greek "metron", meaning limited proportion. This also has a common root with the word "moon" and "month" possibly since the moon and other astronomical objects were among the first measurement methods of time. Some human-referenced units of measurement Units of measurement were among the earliest tools invented by humans. ...


The history of measurements is a topic within the history of science and technology. The metre (U.S.: meter) was standardized as the unit for length after the French revolution, and has since been adopted throughout most of the world. The history of science and technology (HST) is a field of history which examines how humanitys understanding of science and technology has changed over the millennia. ... This article is about the unit of length. ... For other uses, see American English (disambiguation). ... The French Revolution (1789–1815) was a period of political and social upheaval in the political history of France and Europe as a whole, during which the French governmental structure, previously an absolute monarchy with feudal privileges for the aristocracy and Catholic clergy, underwent radical change to forms based on...


Measurement standards

Laws to regulate measurement were originally developed to prevent fraud. However, units of measurement are now generally defined on a scientific basis, and are established by international treaties. In the United States, commercial measurements are regulated by the National Institute of Standards and Technology NIST, a division of the United States Department of Commerce. For other uses, see Law (disambiguation). ... As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ... The United States Department of Commerce is a Cabinet department of the United States government concerned with promoting economic growth. ...


Units and systems of measurement

A baby bottle that measures in all three measurement systems—Imperial (U.K.), U.S. Customary, and metric.
A baby bottle that measures in all three measurement systems—Imperial (U.K.), U.S. Customary, and metric.

The definition or specification of precise standards of measurement involves two key features, which are evident in the International System of Units (SI). Specifically, in this system the definition of each of the base units makes reference to specific empirical conditions and, with the exception of the kilogram, also to other quantitative attributes. Each derived SI unit is defined purely in terms of a relationship involving itself and other units; for example, the unit of velocity is 1 m/s. Due to the fact that derived units make reference to base units, the specification of empirical conditions is an implied component of the definition of all units. The former Weights and Measures office in Middlesex, England. ... A system of measurement is a set of units which can be used to specify anything which can be measured and were historically important, regulated and defined because of trade and internal commerce. ... Image File history File links Metadata Size of this preview: 450 × 600 pixelsFull resolution (800 × 1066 pixel, file size: 221 KB, MIME type: image/jpeg) A baby bottle that displays in all three measurement systems--Metric, Imperial, and U.S. Customary. ... Image File history File links Metadata Size of this preview: 450 × 600 pixelsFull resolution (800 × 1066 pixel, file size: 221 KB, MIME type: image/jpeg) A baby bottle that displays in all three measurement systems--Metric, Imperial, and U.S. Customary. ... “SI” redirects here. ... The former Weights and Measures office in Middlesex, England. ... A central concept in science and the scientific method is that all evidence must be empirical, or empirically based, that is, dependent on evidence or consequences that are observable by the senses. ... SI derived units are part of the SI system of measurement units and are derived from the seven SI base units. ...


Imperial system

Main article: Imperial Unit

Before SI units were widely adopted around the world, the British systems of English units and later Imperial units were used in Britain, the Commonwealth and the United States. The system came to be known as U.S. customary units in the United States and is still in use there and in a few Caribbean countries. These various systems of measurement have at times been called foot-pound-second systems after the Imperial units for distance, weight and time. Many Imperial units remain in use in Britain despite the fact that it has officially switched to the SI system. Road signs are still in miles, yards, miles per hour, and so on, people tend to measure their own height in feet and inches and soda is sold in pints, to give just a few examples. Imperial units are used in many other places, for example, in many Commonwealth countries which are considered metricated, land area is measured in acres and floor space in square feet, particularly for commercial transactions (rather than government statistics). Similarly, the imperial gallon is used in many countries that are considered metricated at gas/petrol stations, an example being the United Arab Emirates. The Imperial units or the Imperial system is a collection of English units, first defined in the Weights and Measures Act of 1824, later refined (until 1959) and reduced. ... The International System of Units (symbol: SI) (for the French phrase Système International dUnités) is the most widely used system of units. ... English unit is the American name for a unit in one of a number of systems of units of measurement, some obsolete, and some still in use. ... The Imperial units or the Imperial system is a collection of English units, first defined in the Weights and Measures Act of 1824, later refined (until 1959) and reduced. ... The Commonwealth of Nations as of 2006 Headquarters Marlborough House, London, UK Official languages English Membership 53 sovereign states Leaders  -  Queen Elizabeth II  -  Secretary-General Don McKinnon (since 1 April 2000) Establishment  -  Balfour Declaration 18 November 1926   -  Statute of Westminster 11 December 1931   -  London Declaration 28 April 1949  Area  -  Total... U.S. customary units, commonly known in the United States as English units or standard units, are units of measurement that are currently used in the U.S., in some cases alongside units from SI (the International System of Units—the modern metric system). ... West Indies redirects here. ... “Miles” redirects here. ... This article is about the unit of measure known as the yard. ... Miles per hour is a unit of speed, expressing the number of international miles covered per hour. ... A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes, ′ – a prime) is a unit of length, in a number of different systems, including English units, Imperial units, and United States customary units. ... Mid-19th century tool for converting between different standards of the inch An inch is an Imperial unit of length. ... The pint is a unit of volume. ...


Metric system

Main article: Metric system

The metric system is a decimalised system of measurement based on the metre and the gram. It exists in several variations, with different choices of base units, though these do not affect its day-to-day use. Since the 1960s the International System of Units (SI), explained further below, is the internationally recognized standard metric system. Metric units of mass, length, and electricity are widely used around the world for both everyday and scientific purposes. The main advantage of the metric system is that it has a single base unit for each physical quantity. All other units are powers of ten or multiples of ten of this base unit. Unit conversions are always simple because they will be in the ratio of ten, one hundred, one thousand, etc. All lengths and distances, for example, are measured in meters, or thousandths of a metre (millimeters), or thousands of meters (kilometres), and so on. There is no profusion of different units with different conversion factors as in the Imperial system (e.g. inches, feet, yards, fathoms, rods). Multiples and submultiples are related to the fundamental unit by factors of powers of ten, so that one can convert by simply moving the decimal place: 1.234 metres is 1234 millimetres or 0.001234 kilometres. The use of fractions, such as 2/5 of a meter, is not prohibited, but uncommon. The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... A system of measurement is a set of units which can be used to specify anything which can be measured and were historically important, regulated and defined because of trade and internal commerce. ... This article is about the unit of length. ... BIC pen cap, about 1 gram. ... The former Weights and Measures office in Middlesex, England. ... Look up si, Si, SI in Wiktionary, the free dictionary. ... Powers of Ten is a 1977 short documentary film written and directed by Charles Eames and his wife, Ray. ... An inch (plural: inches; symbol or abbreviation: in or, sometimes, ″ - a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. ... A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes, ′ – a prime) is a unit of length, in a number of different systems, including English units, Imperial units, and United States customary units. ... This article is about the unit of measure known as the yard. ... A fathom is the name of a unit of length in the Imperial system (and the derived U.S. customary units). ... A rod is a unit of length, equal to 5. ... For other meanings of the word fraction, see fraction (disambiguation) A cake with one quarter removed. ...


SI

The International System of Units (abbreviated SI from the French language name Système International d'Unités) is the modern, revised form of the metric system. It is the world's most widely used system of units, both in everyday commerce and in science. The SI was developed in 1960 from the metre-kilogram-second (MKS) system, rather than the centimetre-gram-second (CGS) system, which, in turn, had many variants. At its development the SI also introduced several newly named units that were previously not a part of the metric system. “SI” redirects here. ... “SI” redirects here. ... French (français, langue française) is one of the most important Romance languages, outnumbered in speakers only by Spanish and Portuguese. ... The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... In physics and metrology, units are standards for measurement of physical quantities that need clear definitions to be useful. ... This article does not cite any references or sources. ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... This article is about the unit of length. ... “Kg” redirects here. ... This article is about the unit of time. ... This article or section is in need of attention from an expert on the subject. ...


There are two types of SI units, Base and Derived Units. Base units are the simple measurements for time, length, mass, temperature, amount of substance, electric current, and light intensity. Derived units are made up of base units, for example density is kg/m3.


Converting prefixes

The SI allows easy multiplication when switching among units having the same base but different prefixes. If you are working with meters and want to convert to centimeters, you only need to multiply the number of meters by 100 because there are 100 centimeters in a meter. Inversely, to switch from centimeters to meters you multiply the number of centimeters by .01.


Length

A 2-metre carpenter's rule
A 2-metre carpenter's rule

A ruler or rule is a tool used in, for example, geometry, technical drawing, engineering, and carpentry, to measure distances or to draw straight lines. Strictly speaking, the ruler is the instrument used to rule straight lines and the calibrated instrument used for determining length is called a measure, however common usage calls both instruments rulers and the special name straightedge is used for an unmarked rule. The use of the word measure, in the sense of a measuring instrument, only survives in the phrase tape measure, an instrument that can be used to measure but cannot be used to draw straight lines. As can be seen in the photographs on this page, a two metre carpenter's rule can be folded down to a length of only 20 centimetres, to easily fit in a pocket, and a five metre long tape measure easily retracts to fit within a small housing. Image File history File links CarpentersRule. ... Image File history File links CarpentersRule. ... A variety of rulers A 2 metre carpenters rule Retractable flexible rule A ruler or rule is an instrument used in geometry, technical drawing and engineering/building to measure distances and/or to rule straight lines. ... For other uses, see Geometry (disambiguation). ... Technical drawing, also known as drafting, is the practice of creating accurate representations of objects for technical, architectural and engineering needs. ...


Time

Main article: Time

The most common devices for measuring time are the clock or watch. A chronometer is a timekeeping instrument precise enough to be used as a portable time standard. Historically, the invention of chronometers was a major advance in determining longitude and an aid in celestial navigation. The most accurate device for the measurement of time is the atomic clock. Look up time in Wiktionary, the free dictionary. ... For other uses, see Clock (disambiguation). ... This article is about portable clocks. ... A chronometer is a timekeeper precise enough to be used as a portable time standard, usually in order to determine longitude by means of celestial navigation. ... Longitude is the east-west geographic coordinate measurement most commonly utilized in cartography and global navigation. ... For the episode of The West Wing, see Celestial Navigation (The West Wing). ... “Nuclear Clock” redirects here. ...


Before the invention of the clock, people measured time using the hourglass, the sundial, and the water clock. For other uses, see Hourglass (disambiguation). ... For other uses, see Sundial (disambiguation). ... A water clock or clepsydra is a device for measuring time by letting water regularly flow out of a container usually by a tiny aperture. ...


Mass

Main article: Weighing scale

Mass refers to the intrinsic property of all material objects to resist changes in their momentum. Weight, on the other hand, refers to the downward force produced when a mass is in a gravitational field. In free fall, objects lack weight but retain their mass. The Imperial units of mass include the ounce, pound, and ton. The metric units gram and kilogram are units of mass. Digital kitchen scales. ... For other uses, see Free-fall (disambiguation). ... The ounce (abbreviation: oz) is the name of a unit of mass in a number of different systems, including various systems of mass that form part of English units, Imperial units, and United States customary units. ... The pound or pound-mass (abbreviations: lb, lbm, or sometimes in the United States, #) is a unit of mass (sometimes called weight in everyday parlance) in a number of different systems, including English units, Imperial units, and United States customary units. ... Look up ton in Wiktionary, the free dictionary. ... BIC pen cap, about 1 gram. ... “Kg” redirects here. ...


A unit for measuring weight or mass is called a weighing scale or, often, simply a scale. A spring scale measures force but not mass, a balance compares masses, but requires a gravitational field to operate. The most accurate instrument for measuring weight or mass is the digital scale, but it also requires a gravitational field, and would not work in free fall.


Difficulties in measurement

Since accurate measurement is essential in many fields, and since all measurements are necessarily approximations, a great deal of effort must be taken to make measurements as accurate as possible. For example, consider the problem of measuring the time it takes for an object to fall a distance of one meter. Using physics, it can be shown that, in the gravitational field of the Earth, it should take any object about .45 seconds to fall one meter. However, the following are just some of the sources of error that arise. First, this computation used for the acceleration of gravity 9.8 meters per second per second. But this measurement is not exact, but only accurate to two significant digits. Also, the Earth's gravitational field varies slightly depending on height above sea level and other factors. Next, the computation of .45 seconds involved extracting a square root, a mathematical operation that required rounding off to some number of significant digits, in this case two significant digits.


So far, we have only considered scientific sources of error. In actual practice, dropping an object from a height of a meter stick and using a stop watch to time its fall, we have other sources of error. First, and most common, is simple carelessness. Then there is the problem of determining the exact time at which the object is released and the exact time it hits the ground. There is also the problem that the measurement of the height and the measurement of the time both involve some error. Finally, there is the problem of air resistance.


Scientific measurements must be carried out with great care to eliminate as much error as possible, and to keep error estimates realistic.


Definitions and theories of measurement

The classical definition of measurement

In the classical definition, which is standard throughout the physical sciences, measurement is the determination or estimation of ratios of quantities. Quantity and measurement are mutually defined: quantitative attributes are those which it is possible to measure, at least in principle. The classical concept of quantity can be traced back to John Wallis and Isaac Newton, and was foreshadowed in Euclid's Elements (Michell, 1993). John Wallis John Wallis (November 22, 1616 - October 28, 1703) was an English mathematician who is given partial credit for the development of modern calculus. ... Sir Isaac Newton FRS (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist. ... The frontispiece of Sir Henry Billingsleys first English version of Euclids Elements, 1570 Euclids Elements (Greek: ) is a mathematical and geometric treatise consisting of 13 books written by the Greek mathematician Euclid in Alexandria circa 300 BC. It comprises a collection of definitions, postulates (axioms), propositions (theorems...


The representational theory of measurement

In the representational theory, measurement is defined as "the correlation of numbers with entities that are not numbers" (Nagel, 1932). The strongest form of representational theory is also known as additive conjoint measurement. In this form of representational theory, numbers are assigned on the basis of correspondences or similarities between the structure of number systems and the structure of qualitative systems. A property is quantitative if such structural similarities can be established. In weaker forms of representational theory, such as that implicit within the work of Stanley Smith Stevens, numbers need only be assigned according to a rule. Stanley Smith Stevens (1906-1973) was an American psychologist best known as the founder of Harvards Psycho-Acoustical Laboratory and credited with the introduction of Stevens power law. ...


The concept of measurement is often misunderstood as merely the assignment of a value, but it is possible to assign a value in a way that is not a measurement in terms of the requirements of additive conjoint measurement. One may assign a value to a person's height, but unless it can be established that there is a correlation between measurements of height and empirical relations, it is not a measurement according to additive conjoint measurement theory. Likewise, computing and assigning arbitrary values, like the "book value" of an asset in accounting, is not a measurement because it does not satisfy the necessary criteria.


Types of measurement proposed by Stevens

The definition of measurement was purportedly broadened by Stanely S. Stevens.[2] He defined types of measurements to include nominal, ordinal, interval and ratio. In practice, this scheme is used mainly in the social sciences but even there its use is controversial because it includes definitions that do not meet the more strict requirements of the classical theory and additive conjoint measurement. However, the classifications of interval and ratio level measurement are not controversial.

  • Nominal: Discrete data which represent group membership to a category which does not have an underlying numerical value. Examples include ethnicity, color, pattern, soil type, media type, license plate numbers, football jersey numbers, etc. May also be dichotomous such as present/absent, male/female, live/dead
  • Ordinal: Includes variables that can be ordered but for which there is no zero point and no exact numerical value. Examples: preference ranks (Thurstone rating scale), Mohs hardness scale, movie ratings, shirt sizes (S,M,L,XL), and college rankings. Also includes the Likert scale used in surveys – strongly agree, agree, undecided, disagree, strongly disagree. Distances between each ordered category are not necessarily the same (a four star movie isn't necessarily just "twice" as good as a two star movie).
  • Interval: Describes the distance between two values but a ratio is not relevant. A numerical scale with an arbitrary zero point. Most common examples Celsius and Fahrenheit. Some consider indexes such as IQ to be interval measurements whereas others consider them only counts. Interval-level measurements can be obtained through application of the Rasch model.
  • Ratio: This is what is most commonly associated with measurements in the physical sciences. The zero value is not arbitrary and units are uniform. This is the only measurement type where ratio comparisons are meaningful. Examples include weight, speed, volume, etc.

The concept of measurement is often confused with counting, which implies an exact mapping of integers to clearly separate objects. IQ redirects here; for other uses of that term, see IQ (disambiguation). ... Rasch models are probabilistic measurement models which currently find their application primarily in psychological and attainment assessment, and are being increasingly used in other areas, including the health profession and market research. ...


Citations

  1. ^ Douglas Hubbard "How to Measure Anything: Finding the Value of Intangibles in Business", John Wiley & Sons, 2007
  2. ^ Stevens, S.S. On the theory of scales and measurement 1946. Science. 103, 677-680.

Miscellaneous

Measuring the ratios between physical quantities is an important sub-field of physics. A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ...


Some important physical quantities include:

The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ... A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin. ... According to the law of universal gravitation, the attractive force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. ... The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... For other uses, see Electron (disambiguation). ... For other uses, see Proton (disambiguation). ... The fine-structure constant or Sommerfeld fine-structure constant, usually denoted , is the fundamental physical constant characterizing the strength of the electromagnetic interaction. ... Quantity is a kind of property which exists as magnitude or multitude. ...

See also

Conversion of units refers to conversion factors between different units of measurement for the same quantity. ... Dimensional analysis is a conceptual tool often applied in physics, chemistry, and engineering to understand physical situations involving a mix of different kinds of physical quantities. ... In dimensional analysis, a dimensionless number (or more precisely, a number with the dimensions of 1) is a pure number without any physical units. ... Econometrics is concerned with the tasks of developing and applying quantitative or statistical methods to the study and elucidation of economic principles. ... Some human-referenced units of measurement Units of measurement were among the earliest tools invented by humans. ... For other uses, see Instrumentation (disambiguation). ... The level of measurement of a variable in mathematics and statistics describes how much information the numbers associated with the variable contain. ... The framework of quantum mechanics requires a careful definition of measurement, and a thorough discussion of its practical and philosophical implications. ... An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. ... For the parapsychology phenomenon of distance knowledge, see psychometry. ... This article is about the field of statistics. ... A system of measurement is a set of units which can be used to specify anything which can be measured and were historically important, regulated and defined because of trade and internal commerce. ... A test method is a definitive procedure that produces a test result. ... Timeline of temperature and pressure measurement technology 1592 - Galileo Galilei builds a crude thermometer using the contraction of air to draw water up a tube 1612 - Santorre Santorio puts thermometer to medical use 1643 - Evangelista Torricelli invents the mercury barometer 1714 - Daniel Gabriel Fahrenheit invents the mercury in glass thermometer... Timeline of time measurement technology 270 BC - Ctesibius builds a popular water clock 46 BC - Julius Caesar and Sosigenes develop a solar calendar with leap years 1000s - Sets of hourglasses were maintained by ships pages to mark the progress of a ship during its voyage 1000s - Large town clocks... The former Weights and Measures office in Middlesex, England. ... In quantum physics, the outcome of even an ideal measurement of a system is not deterministic, but instead is characterized by a probability distribution, and the larger the associated standard deviation is, the more uncertain we might say that that characteristic is for the system. ... “Uncertain” redirects here. ... Virtual Instrumentation is the use of customizable software and modular measurement hardware to create user-defined measurement systems, called virtual instruments. ... Weights and measures is a term used by legal authorities in English speaking countries such as the United Kingdom for a function related to units of measurement in trade. ... In analytical chemistry, the detection limit, or LOD (limit of detection), is the lowest quantity of a substance that can be distinguished from the absence of that substance (a blank value). ... The amount of a single chemical element, a molecular fragment, chemical compound or molecular species that can be reliably (reproducibly) measured after processing a set of spectral data and its associated noise. ... In measurement systems differential linearity refers to a constant relation between the change in the output and input. ...

External links

Look up measurement in Wiktionary, the free dictionary.
  • A Dictionary of Units of Measurement
  • 'Metrology In Short', 2nd Edition
  • Metric conversions
  • Euromet.
  • Measurement Systems.

  Results from FactBites:
 
Units of Measurement (845 words)
We measure the length of a race in meters, but the length of the long jump event in feet and inches.
There are two systems for land measurement (one based on the yard and the other on the rod) and a third system for distances at sea.
In this way, all the units of measurement Americans use every day are based on the standards of the metric system.
measurement. The Columbia Encyclopedia, Sixth Edition. 2001-05 (492 words)
To express a measurement, there must be a basic unit of the quantity involved, e.g., the inch or second, and a standard of measurement (instrument) calibrated in such units, e.g., a ruler or clock.
Measurement, on the other hand, involves entities that may be subdivided into smaller and smaller fractions and is thus always an estimate.
This distinction between measurement and counting seems, on the surface, to break down at the atomic level, where the quantum theory reveals that not only mass (in the form of elementary particles and atoms) but also many other quantities occur only in discrete units, or quanta.
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