How can we be sure that a process is under control? How do we know if the instrument used in the quality control of this industrial process has measurement uncertainty compatible with the required tolerances? Answers to these questions are in determining an acceptance criterion (AC) for the instruments involved in the process and, consequently, in analyzing the calibration certificate of the instruments involved in the quality control of this industrial process. Knowing that the tolerance of a production process is defined as the difference between upper and lower tolerance limits, that is, the maximum variation admitted by the process variables, we need to ensure that these variables are within the measurement range defined by the process.