Under the General Data Protection Regulation (GDPR), the 'main establishment' for a data controller is the "place of its central administration in the Union." This is the location where the ultimate decisions about the purposes and means of data processing are made. In this scenario, the "Company Board and administrative functions" are based in Germany. This indicates that Germany is the center of management and control where strategic decisions concerning data processing activities are taken for the entire company. The locations of retail outlets or specific departments like payroll do not override the location of the central administration as the primary determinant.

A. Belgium: This location has the highest number of retail outlets, indicating significant operational activity, but not the central decision-making authority required to be the main establishment.

B. France: Similar to Belgium, this is a location of operational retail activities, not the company's central administration where strategic data processing decisions are made.

D. Poland: While housing the DPO and a key processing function (payroll), this is an operational site. The location of a DPO is not the determining factor for the main establishment.

1. Regulation (EU) 2016/679 (General Data Protection Regulation), Article 4(16)(a): Defines 'main establishment' for a controller as "the place of its central administration in the Union, unless the decisions on the purposes and means of the processing of personal data are taken in another establishment...and the latter establishment has the power to have such decisions implemented, in which case the establishment where such decisions are taken is to be considered the main establishment."

2. Article 29 Working Party, "Guidelines for identifying a controller or processor’s lead supervisory authority" (WP244 rev.01), 5 April 2017, Section 2.1, page 7: "The GDPR clarifies that for a controller, the main establishment is the place of its central administration in the EU... The place of central administration is not defined in the GDPR but it can be understood as the head office or headquarters of a company where key management and control functions are exercised."

3. Regulation (EU) 2016/679 (General Data Protection Regulation), Recital 36: "The main establishment of a controller in the Union should be determined according to objective criteria and should imply the effective and real exercise of management activities determining the main decisions as to the purposes and means of processing through stable arrangements." The presence of the Company Board in Germany aligns with this recital.