## 1 Introduction
They presented a method based on five steps: Step (a) consists of determining the direction of analysis of measurements of diameter, geometric deviations, and surface roughness and determining the measurement  
Figure 1: Illustration of the idea of \(RE\) for a spur gear [2]. uncertainty in relation to the ISO 286 (_Fundamental Deviation_) standard and/or the ISO 2768 (_General Tolerances_) standard [8]; Step (b) consists of designating the _Sets of candidate IT grades_; Step (c) consists of designating the _Sets of suggested fits_; Step (d), in which the set of suggested fits is limited to obtain the _Sets of preferred fits_; and Step (e) of selecting the best tolerance match relative to production costs. This work contains many mathematical dependencies that determine the zero-one type of behavior (meeting one condition determines a further action, meeting an alternative condition determines a different action). However, you must pay attention to the following facts: (i) gears are tolerated according to other specialized standards regarding the specific method of dimensioning and tolerating the macro- and microgeometry of gears; (ii) gears cannot be referred to as a male or female member of the assembly against which fits are determined; (iii) the issue of the possibility of using statistical techniques to determine the dispersion of measurement data should also be raised; and (iv) the cited work includes measurements using _CMM_. Therefore, there is a need to formulate an adequate tolerance allocation model for gears, using conventional techniques and measuring instruments. Another publication by the same authors, [PERSON] et al. [9] talks about the use of a knowledge-based system (_KBS_) for tolerance allocation in _RE_ and also in relation to the use of CMM in measurements. However, the cited work contains a specific algorithm for assigning tolerances for the tested parts within _RE_ (Figure 3 on page 33), which is the inspiration for the authors of this work to create a tolerance allocation model for gears within _RE_. An aspect contained in the cited work, which the authors considered potentially troublesome in the study of gears, is the use of increments of 0.5 and 0.1 (left side of the algorithm, Figure 3 on page 33 in the cited work) with respect to the _NS_. Even minor manipulations of the base pitch value of the order of thousandths of a millimeter significantly affect the accuracy of recreating the geometry of the tested wheel. Moreover, conventional measuring instruments have much larger error limits than _CMMs_. In [10] by [PERSON] et al., scientists rightly point out that since all parts were received from the original supplier or dismantled from the machines, they have certainly passed quality control by the manufacturer. Therefore, the areas defined by the upper and lower limits of the dimensional values tested should be at least within the original tolerance specifications. However, these types of estimates are conservative because the estimated tolerance areas may be too narrow, which could unnecessarily require high-precision _RE_ manufacturing processes. Four standardized boundary estimators were used to examine a part with nine symmetrically tolerated dimensions and five geometric tolerances: (i) ASME Estimator, (ii) ISO Range Estimator, (iii) ISO 6\(\sigma\) Estimator and (iv) ISO _PCR_ Estimator. As in one of the previously cited works, here the measurements were made using a _CMM_, by which the researchers indicate that the measurement error of a coordinate measuring machine can be approximated by the DGPPR (datum-guided partial Procrustes registration) method proposed by [PERSON] and [PERSON] [11], which is much smaller than the variability between parts. Therefore, measurement errors can be ignored in the study of the tolerance estimation of original manufacturing processes. The presentation of the estimated tolerance fields in the RE process is provided in Tables 1 and 2 of the cited work.