If this situation occurs, the designer should reevaluate whether the tight tolerance is actually required, as it will have economic repercussions. A product s tolerance must be partitioned between the manufacturing variability and the measurement uncertainty associated with verifying conformance to specifications. The optimal allotment of the tolerance between manufacturing and metrology is an economic decision and depends on the equipment available. Manufacturing tools are generally more expensive than metrology equipment, hence, a good calibration for the metrology is a worthwhile investment. Additionally, in manufacturing situations using feedback, such as SPC, a poor calibration that results in a large measurement uncertainty, may cause unnecessary or erroneous adjustment to the manufacturing process and actually degrade product quality.
Calibration is an essential requirement for measurement traceability.
It provides the connection back to the SI unit and supplies an uncertainty statement about the accuracy of the instrument or gage under stated validity conditions. In short, the calibration process tells us what our accuracy is under stated conditions. Unfortunately, actual measurement conditions may differ significantly from those of the calibration. This can make the measurement uncertainty budget difficult to produce, as the calibration information is not directly comparable. In these cases, either a computation is needed that transforms the calibration information into values that are directly comparable to the particular measurement under consideration, or the instrument needs a new calibration that is more relevant to the desired measurement.