Statistical Process Control has taught us to look at and evaluate the variation in processes. More the complexity of the processes more is the potential variation. What we get at the output end is the stacked up variation that is a resultant of variation at every step.
Measurement is a process of evaluating an unknown quantity and expressing it into numbers. The Measurement Process too is subject to all the laws of variation and Statistical Process Control.
Measurement Systems Analysis is the scientific and statistical Analysis of Variation that is induced into the process of measurement.
A measurement system tells us in numerical terms, an important information about the entity that we measure. How sure can we be about the data that the measurement system delivers? Is it the real value of the measure that we obtain out of the measurement process, or is it the measurement system error that we see? Indeed, measurement systems errors can be expensive, and can cost our capability to obtain the true value of what we measure. So, we can say that we can be confident about our reading of a parameter only to the extent that our measurement system can allow.
How does MSA differ from calibration?
It is a standard practice to periodically calibrate all gages and measuring instruments used in measurement on the shop floor.
In simple terms, Calibration is a process of matching up the measuring instrument scale against standards of known value, and correcting the difference, if any. Calibration is done under controlled environment and by specially trained personnel.