3. What about measurement process capability?

Capability studies are subject to a number of difficulties. We'll deal with the question of sampling in the next section, but first and foremost we need to consider the issue of measurement quality. Indeed, it is not enough to calibrate measuring instruments (common practice) for measurements to be sufficiently reliable and, consequently, for the conclusions of the capability study to be relevant.

In the final analysis, the measurement process is a procedure like any other. It too is subject to variations in the conditions under which it is implemented (method, manpower, environment, means, measurand, etc.). As a result, the result it produces (the measurement) is affected by variations in the input parameters. These variations are the source of measurement uncertainty.