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Coming back to the situation of a measurement, we now introduce -
according to GUM - the two definitions:
1) The
best estimate
of the
value of the measurand
is determined from
How uncertainty is determined
its
expectation value
with respect to its associated probability density
distribution.
If this distribution is not known, it can be
estimated as the mean value
from a random sample obtained from repeated measurements.
2) The
standard uncertainty
u of the value of the measurand is determined
as the
positive root of the variance
with respect to its associated
probability density distribution.
If this distribution is not known, the
estimate of the variance of the
mean value
can be used instead.
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