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 the consumer confidence, to the rate of increase in the fall in the price of beanie babies. 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 real-world 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 well-known 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

1 Metrology 2 History 2.1 Systems of measurement 3 Difficulties in measurement 4 See also 5 External links 6 Miscellaneous

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).

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

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)

Miscellaneous

Measuring the ratios between physical quantities is an important sub-field of physics.

Some important physical quantities include:

• the speed of light
• the fine-structure constant
• the charge of an electron

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