A typical tape measure with both metric and imperial units and two US pennies for comparison Contents 1 Methodology 2 Standardization of measurement units 2.1 Standards 3 Units and systems 3.1 Imperial and US customary systems 3.2 Metric system 3.3 International System of Units 3.3.1 Converting prefixes 3.4 Length 3.5 Some special names 3.6 Building trades 3.7 Surveyor's trade 3.8 Time 3.9 Mass 3.10 Economics 3.11 Survey research 4 Difficulties 5 Definitions and theories 5.1 Classical definition
5.2 Representational theory
5.3 Information theory
5.4
6 See also 7 References 8 External links Methodology[edit] The measurement of a property may be categorized by the following criteria: type, magnitude, unit, and uncertainty.[citation needed] They enable unambiguous comparisons between measurements. The type or level of measurement is a taxonomy for the methodological character of a comparison. 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. A unit assigns a mathematical weighting factor to the magnitude that is derived as a ratio to the property of an artifact used as standard or a natural physical quantity. An uncertainty represents the random and systemic errors of the measurement procedure; it indicates a confidence level in the measurement. Errors are evaluated by methodically repeating measurements and considering the accuracy and precision of the measuring instrument. Standardization of measurement units[edit]
Measurements most commonly use the
The seven base units in the SI system. Arrows point from units to those that depend on them. The first proposal to tie an SI base unit to an experimental standard
independent of fiat was by
A baby bottle that measures in three measurement systems—metric, imperial (UK), and US customary. Four measuring devices having metric calibrations Imperial and US customary systems[edit]
Main article: Imperial and US customary measurement systems
Before SI units were widely adopted around the world, the British
systems of
Base quantity Base unit Symbol Current SI constants New SI constants (proposed)[9] time second s hyperfine splitting in Cesium-133 same as current SI length metre m speed of light in vacuum, c same as current SI mass
kilogram
kg
mass of International Prototype
electric current ampere A permeability of free space, permittivity of free space charge of the electron, e temperature kelvin K triple point of water, absolute zero Boltzmann's constant, k amount of substance
mole
mol
molar mass of Carbon-12
luminous intensity candela cd luminous efficacy of a 540 THz source same as current SI The mole was subsequently added to this list and the degree Kelvin renamed the kelvin. There are two types of SI units, base units 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 constructed from the base units, for example, the watt, i.e. the unit for power, is defined from the base units as m2·kg·s−3. Other physical properties may be measured in compound units, such as material density, measured in kg/m3. Converting prefixes[edit] The SI allows easy multiplication when switching among units having 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 divide centimetres by 100. Length[edit] A 2-metre carpenter's ruler See also: List of length, distance, or range measuring devices 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, 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. Some special names[edit] Some non-systematic names are applied for some multiples of some units. 100 kilograms = 1 quintal; 1000 kilogram = 1 metric tonne; 10 years = 1 decade; 100 years = 1 century; 1000 years = 1 millennium Building trades[edit]
The Australian building trades adopted the metric system in 1966 and
the units used for measurement of length are metres (m) and
millimetres (mm).
This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2017) (Learn how and when to remove this template message) 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 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: This computation used for the acceleration of gravity 9.8 metres per second squared (32 ft/s2). But this measurement is not exact, but only precise to two significant digits. The Earth's gravitational field varies slightly depending on height above sea level and other factors. 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. Additionally, other sources of experimental error include: carelessness, determining of the exact time at which the object is released and the exact time it hits the ground, measurement of the height and the measurement of the time both involve some error, Air resistance. Scientific experiments must be carried out with great care to
eliminate as much error as possible, and to keep error estimates
realistic.
Definitions and theories[edit]
Classical definition[edit]
In the classical definition, which is standard throughout the physical
sciences, measurement is the determination or estimation of ratios of
quantities.[11] 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
Airy points
Conversion of units
Detection limit
Differential linearity
Dimensional analysis
Dimensionless number
Econometrics
Electrical measurements
History of measurement
History of science and technology
ISO 10012,
References[edit] ^ a b Pedhazur, Elazar J.; Schmelkin, Liora Pedhazur (1991).
Measurement, Design, and Analysis: An Integrated Approach (1st ed.).
Hillsdale, NJ: Lawrence Erlbaum Associates. pp. 15–29.
ISBN 0-8058-1063-3.
^ a b International Vocabulary of
External links[edit] Look up measurement in Wiktionary, the free dictionary. Wikiquote has quotations related to: Measurement Library resources about Measurement Resources in your library A Dictionary of Units of Measurement
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