63-411: A baseline is a line that is a base for measurement or for construction . The word baseline may refer to: The name Baseline may refer to: It may also refer to: Measurement Measurement is the quantification of attributes of an object or event, which can be used to compare with other objects or events. In other words, measurement is a process of determining how large or small
126-483: A barleycorn . A system of measurement is a collection of units of measurement and rules relating them to each other. As science progressed, a need arose to relate the measurement systems of different quantities, like length and weight and volume. The effort of attempting to relate different traditional systems between each other exposed many inconsistencies, and brought about the development of new units and systems. Systems of units vary from country to country. Some of
189-611: A physical quantity is as compared to a basic reference quantity of the same kind. The scope and application of measurement are dependent on the context and discipline. In 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
252-401: A certain length, nor that a mile is a better measure of distance than a kilometre . Over the course of human history, however, first for convenience and then for necessity, standards of measurement evolved so that communities would have certain common benchmarks. Laws regulating measurement were originally developed to prevent fraud in commerce. Units of measurement are generally defined on
315-458: A digital read-out, but require a gravitational field to function and would not work in free fall. The measures used in economics are physical measures, nominal price value measures and real price measures. These measures differ from one another by the variables they measure and by the variables excluded from measurements. In the field of survey research, measures are taken from individual attitudes, values, and behavior using questionnaires as
378-518: A distance of one metre (about 39 in ). Using physics, it can be shown that, in the gravitational field of the Earth, it should take any object about 0.45 second to fall one metre. However, the following are just some of the sources of error that arise: Additionally, other sources of experimental error include: Scientific experiments must be carried out with great care to eliminate as much error as possible, and to keep error estimates realistic. In
441-460: A few examples. Imperial units are used in many other places, for example, in many Commonwealth countries that are considered metricated, land area is measured in acres and floor space in square feet, particularly for commercial transactions (rather than government statistics). Similarly, gasoline is sold by the gallon in many countries that are considered metricated. The metric system is a decimal system of measurement based on its units for length,
504-440: A filter, changing the quantum state into one with the single measured quantum value. The unambiguous meaning of the quantum measurement is an unresolved fundamental problem in quantum mechanics ; the most common interpretation is that when a measurement is performed, the wavefunction of the quantum system " collapses " to a single, definite value. In biology, there is generally no well established theory of measurement. However,
567-420: A measurement instrument. As all other measurements, measurement in survey research is also vulnerable to measurement error , i.e. the departure from the true value of the measurement and the value provided using the measurement instrument. In substantive survey research, measurement error can lead to biased conclusions and wrongly estimated effects. In order to get accurate results, when measurement errors appear,
630-409: A measurement is an action that determines a particular property (position, momentum, energy, etc.) of a quantum system. Quantum measurements are always statistical samples from a probability distribution; the distribution for many quantum phenomena is discrete. Quantum measurements alter quantum states and yet repeated measurements on a quantum state are reproducible. The measurement appears to act as
693-502: A particular physical object which serves as a standard. Artifact-free definitions fix measurements at an exact value related to a physical constant or other invariable phenomena in nature, in contrast to standard artifacts which are subject to deterioration or destruction. Instead, the measurement unit can only ever change through increased accuracy in determining the value of the constant it is tied to. The first proposal to tie an SI base unit to an experimental standard independent of fiat
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#1732847877634756-498: A property may be categorized by the following criteria: type , magnitude , unit , and uncertainty . They enable unambiguous comparisons between measurements. Measurements most commonly use the International System of Units (SI) as a comparison framework. The system defines seven fundamental units : kilogram , metre , candela , second , ampere , kelvin , and mole . All of these units are defined without reference to
819-424: A quantity may be described as multiples of that of a familiar entity, which can be easier to contextualize than a value in a formal unit system. For instance, a publication may describe an area in a foreign country as a number of multiples of the area of a region local to the readership. The propensity for certain concepts to be used frequently can give rise to loosely defined "systems" of units. For most quantities
882-496: A result, units of measure could vary not only from location to location but from person to person. Units not based on the human body could be based on agriculture, as is the case with the furlong and the acre , both based on the amount of land able to be worked by a team of oxen . Metric systems of units have evolved since the adoption of the original metric system in France in 1791. The current international standard metric system
945-656: A scientific basis, overseen by governmental or independent agencies, and established in international treaties, pre-eminent of which is the General Conference on Weights and Measures (CGPM), established in 1875 by the Metre Convention , overseeing the International System of Units (SI). For example, the metre was redefined in 1983 by the CGPM in terms of the speed of light, the kilogram was redefined in 2019 in terms of
1008-400: A small set of units is required. These units are taken as the base units and the other units are derived units . Thus base units are the units of the quantities which are independent of other quantities and they are the units of length, mass, time, electric current, temperature, luminous intensity and the amount of substance. Derived units are the units of the quantities which are derived from
1071-539: A subject of governmental regulation, to ensure fairness and transparency. The International Bureau of Weights and Measures (BIPM) is tasked with ensuring worldwide uniformity of measurements and their traceability to the International System of Units (SI). Metrology is the science of developing nationally and internationally accepted units of measurement. In physics and metrology, units are standards for measurement of physical quantities that need clear definitions to be useful. Reproducibility of experimental results
1134-433: A unit is necessary to communicate values of that physical quantity. For example, conveying to someone a particular length without using some sort of unit is impossible, because a length cannot be described without a reference used to make sense of the value given. But not all quantities require a unit of their own. Using physical laws, units of quantities can be expressed as combinations of units of other quantities. Thus only
1197-470: 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 kind of quantity . Any other quantity of that kind can be expressed as a multiple of the unit of measurement. For example, a length is a physical quantity . The metre (symbol m) is a unit of length that represents a definite predetermined length. For instance, when referencing "10 metres" (or 10 m), what
1260-448: Is actually meant is 10 times the definite predetermined length called "metre". The definition, agreement, and practical use of units of measurement have played a crucial role in human endeavour from early ages up to the present. A multitude of systems of units used to be very common. Now there is a global standard, the International System of Units (SI), the modern form of the metric system . In trade, weights and measures are often
1323-510: Is an apparently irreversible series of occurrences within this non spatial continuum. It is also used to denote an interval between two relative points on this continuum. 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 , (no net gravitational forces) objects lack weight but retain their mass. The Imperial units of mass include
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#17328478776341386-485: Is central to the scientific method . A standard system of units facilitates this. Scientific systems of units are a refinement of the concept of weights and measures historically developed for commercial purposes. Science , medicine , and engineering often use larger and smaller units of measurement than those used in everyday life. The judicious selection of the units of measurement can aid researchers in problem solving (see, for example, dimensional analysis ). In
1449-409: Is expressed as the product of a numerical value { Z } (a pure number) and a unit [ Z ]: For example, let Z {\displaystyle Z} be "2 metres"; then, { Z } = 2 {\displaystyle \{Z\}=2} is the numerical value and [ Z ] = m e t r e {\displaystyle [Z]=\mathrm {metre} } is the unit. Conversely,
1512-464: Is now defined as exactly 0.0254 m , and the US and imperial avoirdupois pound is now defined as exactly 0.453 592 37 kg . While the above systems of units are based on arbitrary unit values, formalised as standards, natural units in physics are based on physical principle or are selected to make physical equations easier to work with. For example, atomic units (au) were designed to simplify
1575-402: 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. 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
1638-480: Is the International System of Units (abbreviated to SI). An important feature of modern systems is standardization . Each unit has a universally recognized size. Both the imperial units and US customary units derive from earlier English units . Imperial units were mostly used in the British Commonwealth and the former British Empire . US customary units are still the main system of measurement used in
1701-503: Is the conversion of the unit of measurement in which a quantity is expressed, typically through a multiplicative conversion factor that changes the unit without changing the quantity. This is also often loosely taken to include replacement of a quantity with a corresponding quantity that describes the same physical property. One example of the importance of agreed units is the failure of the NASA Mars Climate Orbiter , which
1764-856: The 4th and 3rd millennia BC among the ancient peoples of Mesopotamia , Egypt and the Indus Valley , and perhaps also Elam in Persia as well. Weights and measures are mentioned in the Bible (Leviticus 19:35–36). It is a commandment to be honest and have fair measures. In the Magna Carta of 1215 (The Great Charter) with the seal of King John , put before him by the Barons of England, King John agreed in Clause 35 "There shall be one measure of wine throughout our whole realm, and one measure of ale and one measure of corn—namely,
1827-583: 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 length, weight and time even though the tons, hundredweights, gallons, and nautical miles, for example, are different for
1890-484: The French language name Système International d'Unités ) is the modern revision 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. The SI units for the seven base physical quantities are: In
1953-913: The National Physical Laboratory (NPL), in Australia by the National Measurement Institute , in South Africa by the Council for Scientific and Industrial Research and in India the National Physical Laboratory of India . unit is known or standard quantity in terms of which other physical quantities are measured. Before SI units were widely adopted around the world, the British systems of English units and later imperial units were used in Britain,
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2016-644: The Planck constant and the international yard was defined in 1960 by the governments of the United States, United Kingdom, Australia and South Africa as being exactly 0.9144 metres. In the United States, the National Institute of Standards and Technology ( NIST ), a division of the United States Department of Commerce , regulates commercial measurements. In the United Kingdom, the role is performed by
2079-477: The United States outside of science, medicine, many sectors of industry, and some of government and military, and despite Congress having legally authorised metric measure on 28 July 1866. Some steps towards US metrication have been made, particularly the redefinition of basic US and imperial units to derive exactly from SI units. Since the international yard and pound agreement of 1959 the US and imperial inch
2142-401: The metric system , the imperial system , and United States customary units . Historically many of the systems of measurement which had been in use were to some extent based on the dimensions of the human body. Such units, which may be called anthropic units , include the cubit , based on the length of the forearm; the pace , based on the length of a stride; and the foot and hand . As
2205-403: The ounce , pound , and ton . The metric units gram and kilogram are units of mass. One device 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 weight, both require a gravitational field to operate. Some of the most accurate instruments for measuring weight or mass are based on load cells with
2268-479: 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
2331-492: The social and behavioural sciences , measurements can have multiple levels , which would include nominal, ordinal, interval and ratio scales. Measurement is a cornerstone of trade , science , technology and quantitative research in many disciplines. Historically, many measurement systems existed for the varied fields of human existence to facilitate comparisons in these fields. Often these were achieved by local agreements between trading partners or collaborators. Since
2394-553: The social sciences , there are no standard units of measurement. A unit of measurement is a standardized quantity of a physical property, used as a factor to express occurring quantities of that property. Units of measurement were among the earliest tools invented by humans. Primitive societies needed rudimentary measures for many tasks: constructing dwellings of an appropriate size and shape, fashioning clothing, or bartering food or raw materials. The earliest known uniform systems of measurement seem to have all been created sometime in
2457-448: The 18th century, developments progressed towards unifying, widely accepted standards that resulted in the modern International System of Units (SI). This system reduces all physical measurements to a mathematical combination of seven base units. The science of measurement is pursued in the field of metrology . Measurement is defined as the process of comparison of an unknown quantity with a known or standard quantity. The measurement of
2520-603: The London quart;—and one width of dyed and russet and hauberk cloths—namely, two ells below the selvage..." As of the 21st century, the International System is predominantly used in the world. There exist other unit systems which are used in many places such as the United States Customary System and the Imperial System. The United States is the only industrialized country that has not yet at least mostly converted to
2583-509: The SI, base units are the simple measurements for time, length, mass, temperature, amount of substance, electric current and light intensity. Derived units are constructed from the base units, for example, the watt , i.e. the unit for power, is defined from the base units as m ·kg·s . Other physical properties may be measured in compound units, such as material density, measured in kg/m . The SI allows easy multiplication when switching among units having
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2646-405: The U.S. units. Many Imperial units remain in use in Britain, which has officially switched to the SI system—with a few exceptions such as road signs, which are still in miles. Draught beer and cider must be sold by the imperial pint, and milk in returnable bottles can be sold by the imperial pint. Many people measure their height in feet and inches and their weight in stone and pounds, to give just
2709-414: The base quantities and some of the derived units are the units of speed, work, acceleration, energy, pressure etc. Different systems of units are based on different choices of a set of related units including fundamental and derived units. Following ISO 80000-1 , any value or magnitude of a physical quantity is expressed as a comparison to a unit of that quantity. The value of a physical quantity Z
2772-466: 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 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 . In
2835-500: The crew confusing tower instructions (in metres) and altimeter readings (in feet). Three crew and five people on the ground were killed. Thirty-seven were injured. In 1983, a Boeing 767 (which thanks to its pilot's gliding skills landed safely and became known as the Gimli Glider ) ran out of fuel in mid-flight because of two mistakes in figuring the fuel supply of Air Canada 's first aircraft to use metric measurements. This accident
2898-468: The different systems include the centimetre–gram–second , foot–pound–second , metre–kilogram–second systems, and the International System of Units , SI. Among the different systems of units used in the world, the most widely used and internationally accepted one is SI. The base SI units are the second, metre, kilogram, ampere, kelvin, mole and candela; all other SI units are derived from these base units. Systems of measurement in modern use include
2961-428: The expected value of a quantity, and then, using various methods and instruments, reduces the uncertainty in the value. In this view, unlike the positivist representational theory, all measurements are uncertain, so instead of assigning one value, a range of values is assigned to a measurement. This also implies that there is not a clear or neat distinction between estimation and measurement. In quantum mechanics ,
3024-419: The importance of the theoretical context is emphasized. Moreover, the theoretical context stemming from the theory of evolution leads to articulate the theory of measurement and historicity as a fundamental notion. Among the most developed fields of measurement in biology are the measurement of genetic diversity and species diversity. Units of measurement A unit of measurement , or unit of measure ,
3087-446: The metre and for mass, the kilogram. 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) is the internationally recognised metric system. Metric units of mass, length, and electricity are widely used around the world for both everyday and scientific purposes. The International System of Units (abbreviated as SI from
3150-608: The metric system. The systematic effort to develop a universally acceptable system of units dates back to 1790 when the French National Assembly charged the French Academy of Sciences to come up such a unit system. This system was the precursor to the metric system which was quickly developed in France but did not take on universal acceptance until 1875 when The Metric Convention Treaty was signed by 17 nations. After this treaty
3213-459: The necessary criteria. Three type of representational theory All data are inexact and statistical in nature. Thus the definition of measurement is: "A set of observations that reduce uncertainty where the result is expressed as a quantity." This definition is implied in what scientists actually do when they measure something and report both the mean and statistics of the measurements. In practical terms, one begins with an initial guess as to
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#17328478776343276-425: The numerical value expressed in an arbitrary unit can be obtained as: Units can only be added or subtracted if they are the same type; however units can always be multiplied or divided, as George Gamow used to explain. Let Z {\displaystyle Z} be "2 metres" and W {\displaystyle W} "3 seconds", then There are certain rules that apply to units: Conversion of units
3339-415: 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. Time is an abstract measurement of elemental changes over a non-spatial continuum. It is denoted by numbers and/or named periods such as hours , days , weeks , months and years . It
3402-432: The representational theory, measurement is defined as "the correlation of numbers with entities that are not numbers". The most technically elaborated form of representational theory is also known as additive conjoint measurement . In this form of representational theory, numbers are assigned based on correspondences or similarities between the structure of number systems and the structure of qualitative systems. A property
3465-438: 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
3528-428: The results need to be corrected for measurement errors . The following rules generally apply for displaying the exactness of measurements: 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 an object to fall
3591-515: The same base but different prefixes. To convert from metres to centimetres it is only necessary to multiply the number of metres by 100, since there are 100 centimetres in a metre. Inversely, to switch from centimetres to metres one multiplies the number of centimetres by 0.01 or divides the number of centimetres by 100. A ruler or rule is a tool used in, for example, geometry , technical drawing , engineering, and carpentry, to measure lengths or distances or to draw straight lines. Strictly speaking,
3654-434: The same unit for the distance between two cities and the length of a needle. Thus, historically they would develop independently. One way to make large numbers or small fractions easier to read, is to use unit prefixes . At some point in time though, the need to relate the two units might arise, and consequently the need to choose one unit as defining the other or vice versa. For example, an inch could be defined in terms of
3717-515: The wave equation in atomic physics . Some unusual and non-standard units may be encountered in sciences. These may include the solar mass ( 2 × 10 kg ), the megaton (the energy released by detonating one million tons of trinitrotoluene , TNT) and the electronvolt . To reduce the incidence of retail fraud, many national statutes have standard definitions of weights and measures that may be used (hence " statute measure "), and these are verified by legal officers. In informal settings,
3780-453: Was accidentally destroyed on a mission to Mars in September 1999 (instead of entering orbit) due to miscommunications about the value of forces: different computer programs used different units of measurement ( newton versus pound force ). Considerable amounts of effort, time, and money were wasted. On 15 April 1999, Korean Air cargo flight 6316 from Shanghai to Seoul was lost due to
3843-495: Was by Charles Sanders Peirce (1839–1914), who proposed to define the metre in terms of the wavelength of a spectral line . This directly influenced the Michelson–Morley experiment ; Michelson and Morley cite Peirce, and improve on his method. With the exception of a few fundamental quantum constants, units of measurement are derived from historical agreements. Nothing inherent in nature dictates that an inch has to be
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#17328478776343906-474: Was signed, a General Conference of Weights and Measures (CGPM) was established. The CGPM produced the current SI, which was adopted in 1954 at the 10th Conference of Weights and Measures. Currently, the United States is a dual-system society which uses both the SI and the US Customary system. The use of a single unit of measurement for some quantity has obvious drawbacks. For example, it is impractical to use
3969-549: Was the result of both confusion due to the simultaneous use of metric and Imperial measures and confusion of mass and volume measures. When planning his journey across the Atlantic Ocean in the 1480s, Columbus mistakenly assumed that the mile referred to in the Arabic estimate of 56 + 2 / 3 miles for the size of a degree was the same as the actually much shorter Italian mile of 1,480 metres. His estimate for
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