## 4 Conclusions  
This investigation has managed to analyze the metrological requirements in occupational exposure to vibrations assessment for both estimation- and measurement-based methods. For this, the regulatory framework has been analyzed. European Directive 2002/44 / CE sets the base for such a framework. The CEN--EN ISO 5349-1: 2001, CEN--EN ISO 5349-2: 2001, and CEN--EN ISO 2631-1: 1997 standards arose as references to assess the occupational exposure to vibrations based on measurement-based methods and CEN/TR 15350: 2013 as a reference for the estimation methods. Even if the current regulatory framework considers some metrological aspects regarding the assessment of the level of vibrations, yet many relevant aspects are not considered or established. The estimation-based methods present more important problems than measurement-based methods. The main problems are related to the uncertainty, reliability, and traceability of the results. In this way, the variation between the estimated and the actual values could overestimate the level of exposure to this risk of occupational exposure to vibrations. Regarding the regulatory framework, big differences might appear from one case to another depending on the influences, procedure and features considered in the assessment of the exposure to vibrations. These risk factors can affect the risk assessment results, as operators might be suffering higher or lower levels of vibrations than those estimated. The standards referring to measurement-based methods provide more detailed information than estimation methods on how to proceed when carrying tests, as well as indications on how to determine their uncertainty. Unfortunately, some relevant aspects are unclear or not fully define, and, consequently, manufacturers or users must consider them on their own criteria. This situation does also affect the comparability of the results obtained. When CEN/TR 15350:2013 is applied, in the case were estimation methods, the uncertainty values they are much higher than measurement-based methods. This might lead to an inexact evaluation of the level of vibrations, which will turn into a bad risk assessment. With the new version FprCEN/TR 15350:2020, the daily exposure values have a high level of uncertainty too as well as other unsolved metrological problems in the estimation process. In any case, with the final version of said document (it is currently submitted to the Vote on TR) it will be important to carry out a comparative analysis between versions through future research works. As the European Directive and associated standards indicates, when applying estimation methods input data provided by handbooks, data bases or manufacturers test results might be used. Given the elevated number of different equipment and test codes (and test codes versions) for evaluating them, the available values may vary a lot from one case to another. Furthermore, the values of associated uncertainty are not always included, which makes it difficult to correctly estimate the level of vibrations. These characteristics of the estimation methods make this alternative less useful from a practical and a metrological point of view. No reliable comparison among similar machines and their level of vibrations can be made. Moreover, traceability of the available values cannot be ensured, due to the lack of information on how the procedure employed for obtaining these results or their associated uncertainty. Current regulation regarding exposure to vibrations and its assessment has set the basis for evaluating the different scenarios and machinery that might affect operators. However, it would be interesting to carry out an update of the commented standards, including further details and descriptions about the required procedures, influences to be considered and how to estimate the associated uncertainties to the values provided by manufacturers and the measurements involved. On the other hand, this research has limitations. Among these limitations, the study of a real case is remarkable.