1. Introduction Historically metrologists have attempted to purchase accurate coordinate measuring machines (CMMs) by specifying small values of standardized performance test results such as those defined by the ASME B89.4.1 or ISO 10360 standards. These standardized tests typically involve very simple measurands, such as point-to-point length, measured on highly idealized and geometrically simple artifacts such as gauge blocks, step gauges, and ball bars. While such tests are useful from a commercial transaction viewpoint, i.e., all manufacturers specify their CMM performance to the same tests, which allows easy comparisons between brands, the test results are usually only vaguely indicative of accuracy for the complex tasks that the metrologist performs on CMMs. Consequently, the evaluation of task specific CMM measurement uncertainty was either an outright guess, or a time intensive investigation involving measurements of calibrated artifacts geometrically similar to, and measured in a manner specific to, the task under consideration.