## 2 Background
### Requirements for the Calibration Data Management and Data Formats
#### 2.3.4 Harmonization Challenges for Developing Digital Solutions  
The challenge in developing harmonized and interoperable formats and data exchange between the calibration service providers and the customers is that the requirements for the process and its documentation depend on the roles of the organizations in a calibration chain. For the national metrology institutes (NMI) and accredited laboratories, the calibration practices are mostly defined in the ISO 17025 standard and other requirements that are mandated as a part of the accreditation. However, a significant amount of the calibrations performed in the industry are not done according to the ISO 17025, mostly due to costs. This includes field calibrations that are performed on-site, as this is far more cost-efficient in comparison to having all the process-controlling instruments calibrated at a separate laboratory. For these calibrations, the requirements are defined in the quality management regulations and legislations of the national and regional authorities. Compared to the ISO 17025, which specifically focuses on calibrations, the legislative requirements focus on the quality management system as a whole. The main principles regarding the calibrations of the instruments are no different, but the context and reasoning behind them is. For NMIs and accredited laboratories, calibrations are a service that they provide for their customers, and they are regulated and audited to ensure that their processes are up to the level that is required, and this is why the requirements are very specific. On the other hand, in the industry's end of the calibration chain, the regulations are not as specifically defined in all of the cases. For example, instead of requiring, e.g., calibration processes to follow a specifically defined procedure, the companies are mandated to have written instructions for the processes, meaning that some of the details are left open for the companies to define themselves. Due to this openness, there are some guidelines and good practices that have been adopted as de-facto standards for calibration procedures. To shortly summarize the differences between the regulations for accredited calibrations and field calibrations, accredited calibrations are focused on an individual instrument whereas, in the field calibrations, the instrument is mainly considered as a part of a process line. The effects of these differences in the requirements can be noticed when comparing a typical format for a field calibration certificate to a certificate issued by an accredited laboratory. The field calibration certificates must include information such as the identification of the position or location where the instrument has been used in a particular process line, which is relevant information for the quality assurance of that process line, and a calibration due date based on the calibration interval specified in the manufacturing company's requirements. For the calibration data, the main difference is that the calibration data have been presented in a different way. The standards for the accredited laboratories require that the calibration results are presented including the measurement uncertainties of the measurement points, whereas in the regulations for the industry, it is relatively common that the deviations or measurement errors are required. Another example of these kinds of differences includes requirements for the use of different units in different parts of the world. In addition to the variances in requirements, some challenges for the digitalization of the processes arise from the way in which the requirements have been defined in the standards and legislations, as the current formats are written for human interpretation. The International Electrotechnical Commission (IEC) has presented a utility model for SMART Standards [64]. The model defines the following levels for the digitization degree of a standard:  
* Level 0: Paper format. Not suitable for direct automatic processing or usage.