Traceability and uncertainty estimation in coordinate metrology

National and international standards have defined performance verification procedures for coordinate measuring machines (CMMs) that typically involve their ability to measure calibrated lengths and to a certain extent form. It is recognised that, without further analysis or testing, these results are insufficient to determine the task specific uncertainty of most measurements. Therefore, performance verification methods defined in current standards do not guarantee traceability of measurements performed with a CMM for all measurement tasks, and procedures for the assessment of task-related uncertainties are required. Depending on the requirements for uncertainty level, different approaches may be adopted to achieve traceability. Especially in the case of complex measurement situations and workpieces the procedures are not trivial. This paper discusses the establishment of traceability in coordinate metrology with focus on practical examples, covering simple measurement tasks such as dimension and form as well as complex workpieces such as cylindrical gears and free-form surfaces. The paper illustrates calibration procedures and methods, and the associated obtainable uncertainty level.