2. Measurement Process Characterization 2.1. Characterization 2.1.1. What are the issues for characterization?
'Goodness' of measurements	A measurement process can be thought of as a well-run production process in which measurements are the output. The 'goodness' of measurements is the issue, and goodness is characterized in terms of the errors that affect the measurements.
Bias, variability and uncertainty	The goodness of measurements is quantified in terms of Bias Short-term variability or instrument precision Day-to-day or long-term variability Uncertainty
Requires on-going statistical control program	The continuation of goodness is guaranteed by a statistical control program that controls both Short-term variability or instrument precision Long-term variability which controls bias and day-to-day variability of the process
Scope is limited to on-going processes	The techniques in this chapter are intended primarily for on-going processes. One-time tests and special tests or destructive tests are difficult to characterize. Examples of on-going processes are: Calibration where similar test items are measured on a regular basis Certification where materials are characterized on a regular basis Production where the metrology (tool) errors may be significant Special studies where data can be collected over the life of the study
Application to production processes	The material in this chapter is pertinent to the study of production processes where the size of the metrology (tool) error may be an important consideration. More specific guidance on assessing metrology errors can be found in the section on gauge studies.