Judgment of the Court (Eighth Chamber) of 4 September 2019.#GP v Bundesagentur für Arbeit, Familienkasse Baden-Württemberg West.#Request for a preliminary ruling from the Finanzgericht Baden-Württemberg.#Reference for a preliminary ruling – Social security – Migrant workers – EU rules on currency conversion – Regulation (EC) No 987/2009 – Decision No H3 of the Administrative Commission for the Coordination of Social Security Systems – Calculation of the differential supplement to family allowances that is payable to a worker residing in a Member State and working in Switzerland – Determination of the reference date for the rate of conversion.#Case C-473/18.