## 2 Metrological Study of the Regulatory Framework on the Occupational Exposure to Vibrations
### Measurement-Based Methods
#### 3.2.1 Uncertainty  
It should be noted that in Chapter 7 of the CEN--EN ISO 5349-2:2001 standard, \"Uncertainty in the assessment of daily exposure to vibration\", some metrological aspects are included and considerations regarding measurement uncertainties are introduced. Despite this, the description employs different terminology than is usual in metrological language (e.g., \"factors\" instead of \"influence quantities\") which may generate confusion when estimating such uncertainties. As a result, the described process differs from other standard procedures, and some errors might appear. Although these \"factors\" are suggested, no way of estimating them is specified; in fact, the notes in this section indicate that the uncertainties associated with instruments are usually smaller than others considered, but do not establish a means of estimation. On the other hand, it assumes that the calibration of the instrument itself is one of those influences, however, no information about how to treat its associated uncertainty is provided. * Several investigations have aimed to evaluate the different factors that might appear in real-use condition of the machinery, so that the uncertainty contributions could be determined. In [37], different factors were studied, mainly classified in two types: instrumentation-related factors and non-related. The results showed which factors had a higher influence on the obtained uncertainty, and that some recommendations for reducing it could be exerted and added to the original indications included in the CEN--EN ISO 5349-2:2001 standard (e.g., improvement of adaptors and handles, procedures and periodic calibrations, etc.). For example, in the works [38; 39] there is a very high dispersion of values between tools of the same family or group. However, it would be very interesting to update these results considering the evolution of the machines shown by [28]. * When analyzing daily exposure to vibration, apart from the vibration itself, the other variable to be consider is the exposure time, whose measurement will also have a certain uncertainty associated with it. The CEN/TR 15350:2013 specify a method for its estimation, but with reduced accuracy. * The conditions of the tests for the evaluation of uncertainties are addressed in the Section 6.3 within the CEN--EN ISO 5349-2:2001, entitled \"Checking and verification of the measurement chain\" and within it, in Section 6.3.1 \"Regular checks of functionality\". The need for multiple measurements is specified, which translated into a metrological procedure would be a way of obtaining the contribution of repeatability to the overall uncertainty. However, in the proposed examples it is suggested to change the measurement conditions (using different machine configurations). When this happens, and according to the Guide to the expression of Uncertainty in Measurement (GUM) [40], repeatability cannot be estimated; reproducibility would be obtained instead. Other developments and technologies affected by the treatment of the vibrations measurements are those who aim to improve operator's comfort, by measuring and minimizing the effect of vibrations through specific systems, as in [41]. Such an article presents a new development for seat suspension, where vibrations are measured on site in real time operation, and active dampers aim to reduce it. Again, the measuring system will be affected by the influences mentioned above, and the lack of information might affect the efficiency of the damping system. Other investigations suggest employingavailable measurements together with measurements or information from the secondary vehicle suspension (spring and damper) [42]. Some studies aim to compare the different standards and guidelines in order to set the basis for a common procedure, although, again, they face the problem of comparing data or procedures which may have different operating conditions, data treatment, etc. [43].