# Validation of a Manual Methodology for Measuring Roundness and Cylindicity Tolerances
## 4 Discussion
Thus, the first aspect to consider is the handling of specific instrumentation that requires a valuable learning process for a technician. For example, when the users face a dial comparator, they usually think that this instrument is properly used for measuring length, and they do not guess the final goal inherent in the instrument. Some characteristics, such as sensitivity, resolution, range, and others, are perfectly understood  
Figure 11: Relative error of the roundness tolerance according to the number of points considered in the analysis. Figure 12: Example of a screenshot of a team’s excel spreadsheet. The formulae have been superimposed afterwards. In this example, “,” indicates the decimal point “.”. considering the MM method. On the contrary, the only use of CME does not lead to acquiring these relevant concepts completely. For the assembly to be carried out with V-blocks, it is also fundamental to take into consideration aspects as the geometrical vs. rotation axes, which are hardly visible with CME method. Conclusions are easily drawn about the influence of the V-Blocks on that feature and the way of improving the measuring process. On the other hand, the MM method is essential to guarantee that data management is embedded. Thus, for instance, according to the experience carried out, one of the most highlighted aspects is that drawing the roundness tolerances of a workpiece is difficult to put into practice. Although CME gives directly the real geometric shape of the piece, it is recommended to be capable of building the shape of the workpiece from the numerical data, which must be trained in a specific way. Interpretation of the results is not the same as calculating them, which is something that is completed mechanically from a known formula. From this viewpoint, the MM approach is once again much more robust than the use of CME. In addition, although it is true that cylindricity is difficult to figure out through MM, the different sections of the workpiece measured and interpreted during the practice allowed the gist of this topic to be understood. CME provides a more realistic result of cylindricity, but, again, some aspects can go unnoticed. In Figure 12, an example of the results obtained by a team is shown. In that example, the formulae used are written in an explicit way and they are detailed in Table 1 of Appendix C.  
_Validation of the MM Proposed as a Useful Tool for Measuring Roundness and Cylindricity_  
The problems that the users involved in this research found during the activity, and the corresponding solutions applied, have been summarized in Table 1. Some aspects related to transversal competencies have also been included. The methodology applied was evaluated by Mechanical Engineering students with the aim of checking the suitability and learning results from the user perspective. A satisfaction questionnaire whose questions can be collected into three conceptual dimensions was implemented: relative to the acquisition of the concepts, the suitability of the methodology applied, and the training skills. In Table 2, the questionnaire is shown, indicating after each question the educational dimensions involved, noted as C, M, and S, respectively. As can be observed, some questions take into account more than one dimension. Finally, question 10 is related to a global evaluation of the experience.