Measurement systems include variation and
error, just like any other process. When
a characteristic is measured the readings
that are recorded include this measurement
It is easy to overlook this and assume
that measurements reflect the true value
of the characteristic. This can result in
fruitless attempts to improve the process
when the apparent variation is caused by
variations in the measuring system. Measurement
Systems Analysis should be an essential
precursor to introducing Statistical
Process Control, or using Design
The variation of the measurement system
is generally divided into repeatability
error and reproducibility error, hence Gage
Errors that affect the accuracy of the
measurement include bias, linearity and
The system that establishes
the relationship between a measuring device
and a traceable reference standard. Calibration
may include detecting, correlating, reporting
or eliminating discrepancies in the accuracy
of the measuring instrument.
A standard of known accuracy. The standard
should be traceable to the national standard
of the country concerned. In the United
States that is the National Institute of
Standards and Technology (www.nist.gov).
Gage Repeatability and Reproducibility.
The combined effects of measuring systems
repeatability and reproducibility:
The change in bias over the
operating range of a measuring instrument.
See Measurement Systems Variation.
Short term estimate of the Measurement
See Gage R&R
See Measurement Systems Analysis
See Number of Distinct Categories