## 2 Background  
### Metrology Infrastructure as a Part of the Quality Infrastructure  
The worldwide MI is built upon standards, mutual trust, and recognition between organizations operating around the world [16]. To make the infrastructure as comprehensive as possible, it consists of organizations with different hierarchical roles. At the top of the hierarchy are the national metrology institutes (NMIs) and designated institutes (DI), which maintain the SI system and metrological standards jointly defined by the International Bureau of Weights and Measures (BIPM). Figure 1 presents an illustration of how the MI is established as a part of the QI. The hierarchy of the MI is often depicted in the form of a triangle or pyramid as the amount of measurement instruments and references increases when moving from the NMIs towards the industrial measurement application. A few examples of how the MI has been implemented nationally in European countries are given in [17]. The measurement standards maintained by the NMIs or DIs are referred to as primary standards as their purpose is to provide as accurate and precise physical representations of the unit definitions as possible. Between the industrial applications and primary standards are secondary measurement standards, which are maintained by accredited laboratories and calibrated by the NMIs or DIs. Calibrations are essential to maintain the traceability to SI unit definitions, which ensures the comparability and trustworthiness of measurement results given by individual instruments [8]. Depending on the applications, additional levels of references may also be used in the industry. For example, in the pharmaceutical industry, where the number of instruments used for monitoring and controlling the manufacturing processes can be several thousand per manufacturing site, the use of working standards and travelling standards is common as they provide efficiency in terms of time and costs, e.g., by allowing the calibrations of the process instruments to be carried out on-site. Figure 2 shows an example of a calibration chain from the primary standard of an NMI all the way through to a process instrument of a pharmaceutical manufacturing company. Due to the complexity of the MI and diversity of the organizations involved, the progress of digitalization has been slow and in many cases data are still being managed in paper or paper-on-glass formats requiring human interpretation, e.g., in the case for the documenting of calibrations in calibration certificates [15]. For field calibrations, digitalized solutions have become more common as the costs of calibrations are proportional to the efficiency of the processes. However, these solutions tend to be instrument- and system-provider-specific, and due to competition, the willingness of the system providers to collaborate by harmonizing their systems and making them more open has been low. In addition, it is common that larger industrial companies cooperate with several instrument manufacturers and service providers. Consequently, in the worst case for the instrument owner, the data exchange from different organizations has been  
Figure 1: Metrology infrastructure as a part of the quality infrastructure (QI). Figure 2: An illustration of traceability in a calibration chain. tems and using different formats. Because of this, several human resources relative to the number of annual calibrations have been tied up in the calibration management alone to ensure compliance with the quality management regulation, meaning that it has been a significant expense. As the digitalization in the industry and other sectors is progressing and the collection and use of data is growing rapidly, the topics concerning data quality and trustworthiness become more and more important, which is driving the research and development efforts in digitalization within the metrology community [7, 18].