Measurement

Measurement is the determination of the size or magnitude of something. Measurement is not limited to physical quantities, but can extend to quantifying almost anything imaginable. Examples of measurement range from degrees of uncertainty to consumer confidence to the rate of increase in the fall in the price of a good or service. It is important to know, however, that different kinds of quantity should be measured with different levels of measurement.
In scientific research, measurement is essential. It includes the process of collecting data which can be used to make claims about learning. Measurement is also used to evaluate the effectiveness of a program or product (known as an evaluand).
In physics and engineering, measurement is the process of comparing physical quantities of realworld objects and events. Established standard objects and events are used as units, and the measurement results in at least two numbers for the relationship between the item under study and the referenced unit of measurement, where at least one number estimates the statistical uncertainty in the measurement, also referred to as measurement error (in a philosophical distinction). Measuring instruments are the means by which this translation is made.
For example, the unit for length might be a wellknown person's foot, and the length of a boat can be given as the number of times that person's foot would fit the length of the boat.
 A measurement is a comparison to a standard.  William Shockley
Contents 
Metrology
Metrology is the study of measurement. A metric is a standard for measurement. The quantification of phenomena through the process of measurement relies on the existence of an explicit or implicit metric, which is the standard to which the measure is referenced. If I say I am 5, I am indicating a measurement without supplying an applicable standard. I may mean I am 5 years old or I am 5 feet high, however the implicit metric is that I mean I am 5 years old.
History
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.
The history of measurements is a topic within the history of science and technology. The metre (us: meter) was standardized as the unit for length after the French revolution, and has since been adopted throughout most of the world. The United States and the UK are in the process of converting to the SI system. This process is known as metrication.
Systems of measurement
 SI, also known as the metric system
 Chinese units
 Imperial units
 U.S. customary units
Difficulties in measurement
Measurement of many quantities is very difficult and prone to large error. Part of the difficulty is due to uncertainty, and part of it is due to the limited time available in which to make the measurement.
Examples of things that are very difficult to measure in some respects and for some purposes include social related items such as:
 a person's knowledge (as in testing, see also assessment)
 a person's feelings, emotions, or beliefs.
 a person's senses (qualia).
For even physical quanitities gaining accurate measurement can be difficult. It is not possible to be exact, instead, repeated measurements will vary due to various factors affecting the quantity such as temperature, time, electromagnetic fields, and especially measurement method. As an example in the measurement of the speed of light, the quantity is now known to a high degree of precision due to modern methods, but even with those methods there is some variability in the measurement. Statistical techniques are applied to the measurement samples to estimate the speed. In earlier sets of measurements, the variability was greater, and comparing the results shows that the variability and bias in the measurement methods was not properly taken into account. Proof of this is that when various group's measurements are plotted with the estimated speed and error bars showing the expected variability of the estimated speed from the actual number, the error bars from each of the experiments did not all overlap. This means a number of groups incorrectly accounted for the true sources of error and overestimated the accuracy of their methods.
See also
 units of measurement
 conversion of units
 dimensional analysis
 dimensionless number
 ancient weights and measures
 medieval weights and measures, for historical terms such as league
 levels of measurement
 measurement in quantum mechanics
 orders of magnitude
 timeline of temperature and pressure measurement technology
 timeline of time measurement technology
 uncertainty in measurement
 uncertainty principle
 weights and measures
 econometrics
 instrumentation
Miscellaneous
Measuring the ratios between physical quantities is an important subfield of physics.
Some important physical quantities include:
 the speed of light
 Planck's constant
 the gravitational constant
 the elementary charge (electric charge of electrons, protons, etc.)
 the finestructure constant
External links
 A Dictionary of Units of Measurement (http://www.unc.edu/~rowlett/units/index.html)
 Conversion Calculator (http://www.geocities.com/qubestrader/conversion.html)
 'Metrology In Short', 2nd Edition (http://www.euromet.org/docs/pubs/docs/Metrology_in_short_2nd_edition_may_2004.pdf)bn:পরিমাপ
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