*3.2. Uncertainty of the MMC Calibration, ucal*

Table 2 shows the results indicated by the CMM for every GD&T under study. Thus, it shows the reference result reported by the ZEISS UPMC CARAT CMM in addition to the task-specific uncertainty value (*ucal*) estimated using the ZEISS VCMM™ tool. In this way, the CMM measurement uncertainty for every measured GD&T is assessed, and thus, a task-specific uncertainty budget can be finally accomplished.

For every GD&T element, the highest CMM calibration uncertainty (*ucal*) values are up to 7 μm, whereas the average value is within 1 μm. These results demonstrate that (*ucal*) uncertainty values estimated by the ZEISS VCMM™ tool are consistent with the ZEISS UPMC CARAT CMM Maximum Permissible Error (MPE) specification (0.6 ± L/1000 in μm) although some specific and complex GD&T results are much worse due to the complexity of the evaluation. At this point, the authors made a special effort to understand these results. Thus, a second batch of calibration measurements is performed on the CMM, but the results did not vary significantly, indicating that the obtained results are properly evaluated by the VCMM tool. At this point, the author hypothesises that the source of these results possibly arises from the acquired raw data and employed measuring strategies.


**Table 2.** (*ucal*) uncertainty contributor according to ISO 15530-4 technical specification.
