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viii. approximations and assumptions incorporated in the measurement method and procedure
ix. variations in repeated observations of the measurand under apparently identical conditions
Standard Uncertainty
Uncertainty of the result of a measurement expressed as a standard deviation.
Type A evaluation (of uncertainty)
Method of evaluation of uncertainty by the statistical analysis of series of observations.
Type B evaluation (of uncertainty)
Method of evaluation of uncertainty by means other than the statistical analysis of series of observations.
Note:
a. A Type B evaluation of an uncertainty component is usually based on a pool of comparatively reliable
information. For example,
i. previous measurement data
ii. experience with or general knowledge of the behaviour and properties of relevant materials
and instruments
iii. manufacturer’s specifications
iv. data provided in calibration and other certificates
v. uncertainties assigned to reference data taken from handbooks
Combined Standard Uncertainty
Standard uncertainty of the result of a measurement when that result is obtained from the values of
a number of other quantities, equal to the positive square root of a sum of terms, ther terms being the
variances or covariances of these other quantities weighted according to how the measurement result
varies with changes in these quantities.
Expanded Uncertainty
Quantity defining an interval about the result of a measurement that may be expected to encompass
a large fractions of the distribution of values that could reasonably be attributed to the measurand.
Notes:
a. The fraction may be viewed as the coverage probability or level of confidence of the interval.
b. To associate a specific level of confidence with the interval defined by the expanded uncertainty
requires explicit or implicit assumptions regarding the probablility distribution characterized by
the measurement result and its combined standard uncertainty. The level of confidence that may
be attributed to this interval can be known only to the extent to which such assumptions may be
justified.
c. Expanded uncertain is termed overall uncertainty in paragraph 5 of Recommendation INC-1 (1980).
Coverage Factor
A numerical factor used as a multiplier of the combined standard uncertainty in order to obtain an expanded
uncertainty.
Note:
a. A coverage factor, , is typically in the range 2 to 3.
(Measurable) quantity
Attribute of a phenomenon, body or substance that may be distinguished qualitatively and determined
quantitatively.
Notes:
a. The term quantity m ay refer to a quantity in a general sense or to a particular quantity.
b. Quantities that can be placed in order of magnitude relative to one another are called quantities
of the same kind.
c. Quantities of the same kind may be grouped together into categories of quantities.
Value (of a quantity)
Magnitude of a particular quantity generally expressed as a unit of measurement multiplied by a number
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