# Measurement uncertainty

**uncertaintyerroruncertaintiesuncertainty of measurementmeasurement uncertaintiesamount of uncertaintycertaintydegree of uncertaintyerrors of measurementJCGM**

In metrology, measurement uncertainty is the expression of the statistical dispersion of the values attributed to a measured quantity.wikipedia

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### Metrology

**metrologicalmetrologistlegal metrology**

In metrology, measurement uncertainty is the expression of the statistical dispersion of the values attributed to a measured quantity.

Measurement uncertainty is a value associated with a measurement which expresses the spread of possible values associated with the measurand—a quantitative expression of the doubt existing in the measurement.

### Calibration

**calibratedcalibratecalibrating**

The particular relationship between extension and mass is determined by the calibration of the scale.

This definition states that the calibration process is purely a comparison, but introduces the concept of measurement uncertainty in relating the accuracies of the device under test and the standard.

### Measurement

**measuremeasuringmeasured**

The purpose of measurement is to provide information about a quantity of interest – a measurand.

However, the following are just some of the sources of error that arise:

### Statistical dispersion

**dispersionvariabilityspread**

In metrology, measurement uncertainty is the expression of the statistical dispersion of the values attributed to a measured quantity.

Measurement uncertainty

### Joint Committee for Guides in Metrology

**International Vocabulary of Metrology**

See Joint Committee for Guides in Metrology.

The Guide to the Expression of Uncertainty in Measurement (GUM) is a document published by the JCGM that establishes general rules for evaluating and expressing uncertainty in measurement.

### Probability box

**P-boxesbounds on cumulative distributions**

Distributions of such measurement intervals can be summarized as probability boxes and Dempster–Shafer structures over the real numbers, which incorporate both aleatoric and epistemic uncertainties.

When those data have non-negligible measurement uncertainty represented by interval ranges about each sample value, an empirical distribution may be generalized to a p-box.

### Standard deviation

**standard deviationssample standard deviationsigma**

All measurements are subject to uncertainty and a measurement result is complete only when it is accompanied by a statement of the associated uncertainty, such as the standard deviation.

### Mean

**mean valuepopulation meanaverage**

This particular single choice is usually called the measured value, which may be optimal in some well-defined sense (e.g., a mean, median, or mode).

### Median

**averagesample medianmedian-unbiased estimator**

This particular single choice is usually called the measured value, which may be optimal in some well-defined sense (e.g., a mean, median, or mode).

### Mode (statistics)

**modemodalmodes**

This particular single choice is usually called the measured value, which may be optimal in some well-defined sense (e.g., a mean, median, or mode).

### Quantity

**quantitiesquantitativeamount**

The purpose of measurement is to provide information about a quantity of interest – a measurand.

### Volume

**volumetriccapacityvolumes**

For example, the measurand might be the size of a cylindrical feature, the volume of a vessel, the potential difference between the terminals of a battery, or the mass concentration of lead in a flask of water.

### Voltage

**potential differenceVvoltages**

For example, the measurand might be the size of a cylindrical feature, the volume of a vessel, the potential difference between the terminals of a battery, or the mass concentration of lead in a flask of water.

### Mass concentration (chemistry)

**mass concentrationw/vmg/dL**

For example, the measurand might be the size of a cylindrical feature, the volume of a vessel, the potential difference between the terminals of a battery, or the mass concentration of lead in a flask of water.

### Average

**Rushing averageReceiving averagemean**

Their average would provide an estimate of the true value of the quantity that generally would be more reliable than an individual measured value.

### ASME

**American Society of Mechanical EngineersAmerican Society of Mechanical Engineers (ASME)Fellow**

The American Society of Mechanical Engineers (ASME) has produced a suite of standards addressing various aspects of measurement uncertainty.

### ISO/IEC 17025

**ISO 17025ISO/IEC 17025:200517025**

The GUM has been adopted by all major National Measurement Institutes (NMIs), by international laboratory accreditation standards such as ISO/IEC 17025 General requirements for the competence of testing and calibration laboratories which is required for international laboratory accreditation, and employed in most modern national and international documentary standards on measurement methods and technology.

### International Laboratory Accreditation Cooperation

**ILACaccreditedILAC (International Laboratory Accreditation Cooperation)**

The GUM has been adopted by all major National Measurement Institutes (NMIs), by international laboratory accreditation standards such as ISO/IEC 17025 General requirements for the competence of testing and calibration laboratories which is required for international laboratory accreditation, and employed in most modern national and international documentary standards on measurement methods and technology.

### Mass

**inertial massgravitational massweight**

For example, the bathroom scale may convert a measured extension of a spring into an estimate of the measurand, the mass of the person on the scale.

### Mathematical model

**modelmathematical modelingmathematical models**

A measurement model converts a quantity value into the corresponding value of the measurand.

### Buoyancy

**buoyantbuoyant forcefloat**

Alternatively, a more sophisticated model of a weighing, involving additional effects such as air buoyancy, is capable of delivering better results for industrial or scientific purposes.

### Temperature

**temperaturesair temperaturewarm**

In general there are often several different quantities, for example temperature, humidity and displacement, that contribute to the definition of the measurand, and that need to be measured.

### Humidity

**humidspecific humidityair humidity**

In general there are often several different quantities, for example temperature, humidity and displacement, that contribute to the definition of the measurand, and that need to be measured.

### Displacement (vector)

**displacementdisplacement vectordisplacements**

In general there are often several different quantities, for example temperature, humidity and displacement, that contribute to the definition of the measurand, and that need to be measured.

### Physical constant

**constantconstantsuniversal constant**

Some such data relate to quantities representing physical constants, each of which is known imperfectly.